 | MASUI TakahikoDepartment of Science Associate Professor | ||
Last Updated :2024/05/19
Researcher Information
Degree
J-Global ID
Research Interests
- Raman spectrum solid state physics superconductivity
Research Areas
Published Papers
- Hideaki Iwasawa; Tetsuro Ueno; Takahiko Masui; Setsuko Tajimanpj Quantum Materials Springer Science and Business Media LLC 7 (1) 2022/12 [Refereed]
Abstract Spatial inhomogeneity on the electronic structure is one of the vital keys to provide a better understanding of the emergent quantum phenomenon. Given the recent developments on spatially resolved ARPES (ARPES: angle-resolved photoemission spectroscopy), the information on the spatial inhomogeneity on the local electronic structure is now accessible. However, the next challenge becomes apparent as the conventional analysis encounters difficulty handling a large volume of a spatial mapping dataset, typically generated in the spatially resolved ARPES experiments. Here, we propose a machine-learning-based approach using unsupervised clustering algorithms (K-means and fuzzy-c-means) to examine the spatial mapping dataset. Our analysis methods enable automated categorization of the spatial mapping dataset with a much-reduced human intervention and workload, thereby allowing quick identification and visualization of the spatial inhomogeneity on the local electronic structures. - Kiyohisa Tanaka; NguyenTrung Hieu; Giulio Vincini; Takahiko Masui; Shigeki Miyasaka; Setsuko Tajima; Takao SasagawaJournal of the Physical Society of Japan 88 (4) 044710-1 - 044710-6 2019/04 [Refereed]
- Hideaki Iwasawa; Pavel Dudin; Kyosuke Inui; Takahiko Masui; Timur K. Kim; Cephise Cacho; Moritz HoeschPhysical Review B 99 (14) 140510(R)-1 - 140510(R)-6 2019/04 [Refereed]
- H. Iwasawa; N. B; M. Schroter; T. Masui; S Tajima; T. K. Kim; M HoeschPhysical Review B 98 (8) 081112(R)-1 - 081112(R)-6 2018/08 [Refereed]
- Hirofumi Kawanaka; Yoshihiro Aiura; Takayuki Hasebe; Makoto Yokoyama; Takahiko Masui; Yoshikazu Nishihara; Takashi YanagisawaSCIENTIFIC REPORTS NATURE PUBLISHING GROUP 6 35150-1 - 35150-6 2045-2322 2016/10 [Refereed]
The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature T-c of 160 K is studied. We observed for the first time a shift of Delta T-c similar to 1 K by oxygen isotope substitution of O-16 -> O-18 in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient alpha = -partial derivative ln T-c/partial derivative lnM. The Raman spectra indicate that the main vibration frequency of O-16 at 363 cm(-1) shifts to 341 cm(-1) following oxygen isotope substitution O-18. This shift is remarkably consistent with the Debye frequency being proportional to proportional to 1 root M where M is the mass of an oxygen atom. The positive isotope shift of Delta T-c can be understood by taking account of the electron-phonon interaction. - N. Murai; T. Masui; M. Ishikado; S. Ishida; H. Eisaki; S. Uchida; S. TajimaPhysical Review B - Condensed Matter and Materials Physics American Physical Society 91 (21) 1550-235X 2015/06 [Refereed]
We report Raman scattering measurements on Bi2Sr2CaCu2O8+δ single crystals with a different degree of out-of-plane disorder to examine the effect of Tc change on the the electronic Raman response at the optimal doping level. The B1g peak energies for lower Tc disordered samples are essentially independent of Tc. However, a further increase of Tc by minimizing the degree of out-of-plane disorder leads to a high-energy shift of the B1g peak. Interestingly, abrupt change of the B1g peak energy occurs when the the superconducting gap energy exceeds the pseudogap energy, which results in the recovery of superconductivity-dominated Raman response in B1g symmetry. It suggests that these anomalous properties of the antinodal electrons are a consequence of the unconventional superconducting state of the cuprates where superconductivity coexists with the pseudogap in the ground state. - N. Murai; T. Masui; M. Ishikado; S. Ishida; H. Eisaki; S. Uchida; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 91 (21) 214520-1 - 214520-6 2469-9950 2015/06 [Refereed]
We report Raman scattering measurements on Bi2Sr2CaCu2O8+delta single crystals with a different degree of out-of-plane disorder to examine the effect of T-c change on the the electronic Raman response at the optimal doping level. The B-1g peak energies for lower T-c disordered samples are essentially independent of T-c. However, a further increase of T-c by minimizing the degree of out-of-plane disorder leads to a high-energy shift of the B-1g peak. Interestingly, abrupt change of the B-1g peak energy occurs when the the superconducting gap energy exceeds the pseudogap energy, which results in the recovery of superconductivity-dominated Raman response in B-1g symmetry. It suggests that these anomalous properties of the antinodal electrons are a consequence of the unconventional superconducting state of the cuprates where superconductivity coexists with the pseudogap in the ground state. - Ece Uykur; Kiyohisa Tanaka; Takahiko Masui; Shigeki Miyasaka; Setsuko TajimaPHYSICAL REVIEW LETTERS AMER PHYSICAL SOC 112 (12) 127003-1 - 127003-5 0031-9007 2014/03 [Refereed]
The superconductivity precursor phenomena in high temperature cuprate superconductors is studied by direct measurements of the superconducting condensate with the use of the c-axis optical conductivity of YBa2(Cu1-xZnx)(3)O-y for several doping levels (p) as well as for several Zn concentrations. Both the real and imaginary parts of the optical conductivity clearly show that the superconducting carriers persist up to the high temperatures T-p that is higher than the critical temperature T-c but lower than the pseudogap temperature T*. T-p increases with reducing doping level like T*, but decreases with Zn substitution unlike T*. - K. Kamiya; T. Masui; S. Tajima; H. Bando; Y. AiuraPHYSICAL REVIEW B AMER PHYSICAL SOC 89 (6) 060505(R)-1 - 060505(R)-4 1098-0121 2014/02 [Refereed]
We have prepared oxygen isotope exchanged crystals of impurity-free YBa2Cu3Oy with various oxygen contents, and examined pure doping (p) dependence of isotope effect on superconducting transition temperature. With decreasing oxygen contents, the isotope exponent alpha monotonously increases without any anomaly around p = 1/8. The monotonous increase in alpha indicates that phonons are involved in the mechanism which causes the monotonous T-c suppression with underdoping. - Ece Uykur; Kiyohisa Tanaka; Takahiko Masui; Shigeki Miyasaka; Setsuko TajimaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN PHYSICAL SOC JAPAN 82 (3) 033701-1 - 033701-4 0031-9015 2013/03 [Refereed]
To address the issue of the pseudogap in the superconducting state of the high temperature superconducting cuprates, we studied the temperature dependent redistribution of the spectral weight in the c-axis polarized optical spectra for underdoped YBa2(Cu1-xZnx)(3)O7-delta single crystals with x = 0, 0.007, 0.012, and 0.04. It was found that for Zn substituted samples, the spectral weight transfer to the high energy region, which characterizes the pseudogap state, continues even below the superconducting transition temperature (T-c), indicating the coexistence of the pseudogap and the superconducting gap. Moreover, the observation of the pseudogap in the Zn-doped non-superconducting sample gives evidence that the pseudogap is not a precursor of superconductivity. - E. Uykur; K. Tanaka; T. Masui; S. Miyasaka; S. TajimaPROCEEDINGS OF THE 25TH INTERNATIONAL SYMPOSIUM ON SUPERCONDUCTIVITY (ISS2012) ELSEVIER SCIENCE BV 45 45 - 48 1875-3892 2013 [Refereed]
To clarify recent discussions on the precursor superconducting state in high-T-c cuprates, we performed a temperature dependent c-axis optical study on YBa2(Cu1-xZnx)O-y single crystals in the pseudogap region for several different Zn-contents (x = 0, 0.007, 0.012, and 0.04) and doping levels. The superfluid density calculation revealed a third temperature scale (T-p) for a precursor superconducting state in between the superconducting transition temperature, T-c, and the pseudogap opening temperature, T*. We observed the suppression and the disappearance of T-p with increasing Zn-content, which is further evidence of the close relation between the origin of T-c and T-p. (C) 2013 The Authors. Published by Elsevier B.V. - N. T. Hieu; K. Tanaka; T. Masui; S. Miyasaka; S. Tajima; T. SasagawaPhysics Procedia Elsevier B.V. 45 41 - 44 1875-3892 2013 [Refereed]
In this paper we present the calculations of electronic Raman scattering (ERS) spectra for B1g and B2g geometries using angleresolved photoemission spectroscopy (ARPES) spectra of nearly optimally doped cuprate superconductor Bi2Sr2CaCu2O 8 (Bi2212), Tc=92K. Calculations were taken on the Fermi surface (FS) in the superconducting state at temperature well below T c and the results were quantitatively compared to the experimental data. It shows that there is a good agreement in B1g while the peak position in B2g is about 100 cm-1 lower than the experimental one. This result indicates that the scattering rate is not large enough to explain Raman spectra and additional contribution should be taken into account to reproduce ERS spectra. © 2013 The Authors. - N. Murai; T. Masui; M. Ishikado; S. Ishida; H. Eisaki; S. Uchida; S. TajimaPhysics Procedia Elsevier B.V. 45 37 - 40 1875-3892 2013 [Refereed]
We measured electronic Raman spectra of nonstoichiometric Bi 2+xSr2-xCaCu2O8+awith x=0.1, 0.3 and stoichiometric Bi2Sr2Y0.08Ca 0.92Cu2O8+a and investigated the effect of out-of-plane disorder on the superconducting B1g Raman response. We observed that the B1g peak energy is enhanced in Y-substituted Bi2212, compared with that in nonstoichiometric Bi2212. By contrast, for nonstoichiometric Bi2212, the B1g peak energy remains constant, even if Tc is significantly suppressed by disorder. This anomalous behavior is discussed in terms of the interplay between the pseudogap and superconducting gap. © 2013 The Authors. - Ece Uykur; Kiyohisa Tanaka; Takahiko Masui; Shigeki Miyasaka; Setsuko TajimaJournal of the Physical Society of Japan Physical Society of Japan 81 SB035-1 - SB035-4 1347-4073 2012 [Refereed]
In this study we present the temperature dependent E//c-axis optical spectra of the underdoped YBa2Cu3O7-δ single crystals for x = 0 and 0.007. In addition to the shift of Josephson plasma edge, the spectral structures due to the transverse Josephson plasma mode have been suppressed with Zn-doping. Owing to the absence of these modes, we successfully observed the continuous spectral weight transfer to the high energy region below a superconducting transition temperature (Tc), which leads to the conclusion that the pseudogap state and the superconducting gap coexist below Tc. © 2012 The Physical Society of Japan. - N. Murai; T. Masui; M. Ishikado; S. Ishida; H. Eisaki; S. Uchida; S. TajimaJournal of the Physical Society of Japan Physical Society of Japan 81 SB033-1 - SB033-4 1347-4073 2012 [Refereed]
We report electronic Raman scattering measurements on out-of-plane disordered Bi2+xSr2-xCaCu2O 8+δ. With increasing out-of-plane disorder, the critical temperature Tc is significantly suppressed, but suppression of the superconducting gap energy is observed only in the nodal region. Our experimental finding advocate the two-gap scenario that the origins of the nodal and the antinodal gap are different. © 2012 The Physical Society of Japan. - N. Murai; T. Masui; M. Ishikado; S. Ishida; H. Eisaki; S. Uchida; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 85 (2) 20507(R)-1 - 20507(R)-4 1098-0121 2012/01 [Refereed]
We report a systematic study of the variation of electronic Raman spectra as a function of disorder for Bi2+xSr2-xCaCu2O8+delta with different Bi:Sr nonstoichiometry. We have observed that, with increasing disorder, the suppression of the superconducting gap is observed only in the nodal region, while there is no change in the antinodal gap. This dichotomy of the response to disorder in the nodal and the antinodal gap can be interpreted as evidence for different origins of these two gaps. - E. Uykur; K. Tanaka; T. Masui; S. Miyasaka; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 84 (18) 1098-0121 2011/11 [Refereed]
We measured the temperature dependence of the in-plane polarized reflectivity spectra of twin-free Y1-xCaxBa 2Cu3O7-δ single crystals with different Ca concentrations (x=0,0.11,and 0.16) from the optimally doped to heavily overdoped region. Low-energy optical conductivity spectra showed a Drude-like residual conductivity at temperatures far below the superconducting transition temperature, which indicates the presence of unpaired-normal carriers in the superconducting state. Comparing the spectra at a fixed Ca content or at a fixed doping level, we have revealed that the carrier overdoping increases unpaired carriers in addition to those induced by the Ca disorder. We also found the superconducting behavior of the one-dimensional CuO chains for the Ca-free samples. © 2011 American Physical Society. - E. Uykur; K. Tanaka; T. Masui; S. Miyasaka; S. TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 471 (21-22) 701 - 703 0921-4534 2011/11 [Refereed]
In this study we present the temperature dependent E//a-axis optical conductivity spectra of detwinned Y1-xCaxBa2Cu3Oy single crystals (x = 0, 0.11 and 0.16) in the optimally doped and overdoped region. The optical conductivity spectra show Drude like residual conductivity, in the far-infrared region, even well below the superconducting transition temperature, which indicates the increase of the non-superconducting component at the superconducting regime. The origin of the residual conductivity can be either carrier-overdoping or pair-breaking effects due to Ca-disorder. Comparing the spectra for various Ca-content at the optimum doping, we found that Ca-substitution enhances the residual conductivity. In addition, from comparison of the spectra in the optimally doped and overdoped samples at a fixed Ca-content, we can conclude that there is an intrinsic overdoping effect of the residual conductivity. (C) 2011 Elsevier B.V. All rights reserved. - E. Uykur; K. Tanaka; T. Masui; S. Miyasaka; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 84 (18) 184527-1 - 184527-7 2469-9950 2011/11 [Refereed]
We measured the temperature dependence of the in-plane polarized reflectivity spectra of twin-free Y1-xCaxBa2Cu3O7-delta single crystals with different Ca concentrations (x = 0, 0.11, and 0.16) from the optimally doped to heavily overdoped region. Low-energy optical conductivity spectra showed a Drude-like residual conductivity at temperatures far below the superconducting transition temperature, which indicates the presence of unpaired-normal carriers in the superconducting state. Comparing the spectra at a fixed Ca content or at a fixed doping level, we have revealed that the carrier overdoping increases unpaired carriers in addition to those induced by the Ca disorder. We also found the superconducting behavior of the one-dimensional CuO chains for the Ca-free samples. - Rongchao Ma; K. H. Chow; J. Jung; D. Prabhakaran; H. Tadatomo; T. Masui; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 83 (21) 212504-1 - 212504-4 1098-0121 2011/06 [Refereed]
Temperature and magnetic field dependence of the vortex penetration into a superconductor and the resulting trapped vortex field (the vortex remanent state) were investigated for Bi2Sr2CaCu2O8+x (BSCCO) and YBa2Cu3O6+x (YBCO) single crystals and BSCCO thin films. The experiments revealed changes in the pinning regime (the magnitude and magnetic relaxation) of the trapped vortex field with an increasing temperature. The trapped vortex field, obtained by applying a constant magnetic field, exhibits a maximum at a certain temperature, that separates the partial vortex penetration regime at low temperatures from the complete vortex penetration state at higher temperatures. The corresponding vortex remanent states in these two regimes are characterized by two distinctly different relaxations, the logarithmic and the nonlogarithmic ones at temperatures below and above the maximum, respectively, for both BSCCO and YBCO. At temperatures close to T-c surface/geometric barrier affect the relaxation rates. - M. Okawa; K. Ishizaka; H. Uchiyama; H. Tadatomo; T. Masui; S. Tajima; X-Y. Wang; C-T. Chen; S. Watanabe; A. Chainani; T. Saitoh; S. ShinPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 470 (Supplement 1) S62 - S64 0921-4534 2010/12 [Refereed]
We investigate the bulk superconducting electronic structure in optimally doped YBa2Cu3O7-delta (YBCO) using laser-excited angle-resolved photoemission spectroscopy. The band dispersions with the d(x2-y2)-wave like gap opening are observed without being hindered by surface state and CuO chain band due to bulk-sensitivity and/or matrix element effect at hv = 6.994 eV. The momentum-dependence of the superconducting gap exhibits a nonzero minimum of similar to 12 meV along the (0,0) (pi,pi) line. In addition, the unusual suppression of the quasiparticle coherence is observed at T/T-c > 0.5-0.7. (C) 2009 Elsevier B.V. All rights reserved. - H. Iwasawa; J. F. Douglas; K. Sato; T. Masui; Y. Yoshida; Z. Sun; H. Eisaki; H. Bando; A. Ino; M. Arita; K. Shimada; H. Namatame; M. Taniguchi; S. Tajima; S. Uchida; T. Saitoh; D. S. Dessau; Y. AiuraPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 470 (Supplement 1) S134 - S136 0921-4534 2010/12 [Refereed]
Using angle-resolved photoemission spectroscopy (ARPES) with low-energy tunable photons, we studied the oxygen isotope effect in optimally doped Bi2Sr2CaCu2O8+delta (Bi2212). We found the oxygen isotope shift in the real part of the electron self-energies [Re Sigma(omega)s] along the nodal direction derived not only from the momentum distribution curves (MDCs) but also from the energy distribution curves (EDCs). Present results indicate straightforwardly the coupling between the nodal electrons and the phonons. (C) 2009 Published by Elsevier B.V. - T. Masui; Y. Mikasa; S. Lee; S. TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 470 (Supplement 1) S627 - S628 0921-4534 2010/12 [Refereed]
Pressure effects on resistivity for C- and Al-substituted MgB2 single crystals are reported. It is seen that resistivities at high temperatures are suppressed for Al-substituted sample, while resistivity does not change for C-substituted samples, suggesting different introduction of impurity scattering. (C) 2009 Elsevier B.V. All rights reserved. - H. Tadatomo; T. Masui; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 82 (22) 1098-0121 2010/12 [Refereed]
We report temperature dependences of B1g electronic Raman spectra in slightly underdoped YBa2 Cu3 O 7-δ samples. Above Tc, we found no signature associated with the pseudogap while below Tc we can acquire superconductivity-induced peaks which shift to higher energy with decreasing hole concentration (p) and disappear at p=0.11. These behaviors are similar to those reported for other cuprates. The unusual properties of the antinodal electrons are discussed in comparison with the angle-resolved photoemission spectra. © 2010 The American Physical Society. - H. Tadatomo; T. Masui; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 82 (22) 224503-1 - 224503-5 2469-9950 2010/12We report temperature dependences of B-1g electronic Raman spectra in slightly underdoped YBa2Cu3O7-delta samples. Above T-c, we found no signature associated with the pseudogap while below T-c we can acquire superconductivity-induced peaks which shift to higher energy with decreasing hole concentration (p) and disappear at p=0.11. These behaviors are similar to those reported for other cuprates. The unusual properties of the antinodal electrons are discussed in comparison with the angle-resolved photoemission spectra.
- Takahiko Masui; Yuji Mikasa; Sergey Lee; Setsuko TajimaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN PHYSICAL SOC JAPAN 79 (7) 074719-1 - 074719-5 0031-9015 2010/07Pressure effects on resistivity, T-c, and H-c2 for pure, and C- and Al-substituted MgB2 single crystals are reported. While the suppression behavior of T-c [Delta T-c/T-c(0)] does not markedly differ among the samples, a large difference is seen in the suppression of the resistivity slope at high temperatures. This suggests that the strength of interband scattering differs between C- and Al-substituted samples.
- K. Sato; H. Iwasawa; N. C. Plumb; T. Masui; Y. Yoshida; H. Eisaki; H. Bando; A. Ino; M. Arita; K. Shimada; H. Namatame; M. Taniguchi; S. Tajima; Y. Nishihara; D. S. Dessau; Y. AiuraPHYSICAL REVIEW B AMER PHYSICAL SOC 80 (21) 212501-1 - 212501-4 1098-0121 2009/12 [Refereed]
The disorder dependence of the oxygen isotope effect in optimally doped Bi(2)Sr(1.6)Ln(0.4)CuO(6+delta) superconductors which is introduced into cation sites in the planes adjacent to CuO2 planes is studied. The degree of out-of-plane disorder is controlled by substituting Ln ions with different ionic radii from La to Gd. This type of disorder does not explicitly alter the nodal electronic structure or the underlying Fermi surface but markedly enhances the oxygen isotope exponent at the superconducting transition temperature (alpha(Tc)). The enhancement in alpha(Tc) is well explained by the pair-breaking model, suggesting the growth of a pseudogap state around the antinodal region due to the out-of-plane disorder. - M. Okawa; K. Ishizaka; H. Uchiyama; H. Tadatomo; T. Masui; S. Tajima; X. -Y. Wang; C. -T. Chen; S. Watanabe; A. Chainani; T. Saitoh; S. ShinPHYSICAL REVIEW B AMER PHYSICAL SOC 79 (14) 144528-1 - 144528-9 1098-0121 2009/04 [Refereed]
Low-energy electronic structure of optimally doped YBa2Cu3O7-delta is investigated using laser-excited angle-resolved photoemission spectroscopy. The surface state and the CuO chain band that usually overlap the CuO2 plane derived bands are not detected, thus enabling a clear observation of the bulk superconducting state. The observed bilayer splitting of the Fermi surface is similar to 0.08 A(-1) along (0,0)-(pi,pi) direction, significantly larger than Bi2Sr2CaCu2O8+delta. The kink structure of the band dispersion reflecting the renormalization effect at similar to 60 meV shows up similarly as in other hole-doped cuprates. The momentum dependence of the superconducting gap shows d(x)(2)-y(2)-wave-like amplitude but exhibits a nonzero minimum of similar to 12 meV along the (0,0)-(pi,pi) direction. Possible origins of such an unexpected "nodeless" gap behavior are discussed. - A. I. Buzdin; A. S. Mel'nikov; A. V. Samokhvalov; T. Akashi; T. Masui; T. Matsuda; S. Tajima; H. Tadatomo; A. TonomuraPHYSICAL REVIEW B AMER PHYSICAL SOC 79 (9) 094510-1 - 094510-5 1098-0121 2009/03 [Refereed]
In thin films of anisotropic superconductors, the intervortex interaction may be strongly modified because of the interplay between the long-ranged repulsion caused by an extremely slow decay of the supercurrent induced by a single vortex line (Pearl's effect) and the attraction caused by the tilt of the vortex lines with respect to the anisotropy axes. We present a theoretical analysis and Lorentz microscopy experimental data for high-temperature superconducting cuprates which provide evidence of such interplay. Moreover we report on a theoretical prediction of a very special type of the vortex arrangement-the formation of the vortex molecules. - T. Masui; T. Hiramachi; K. Nagasao; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 79 (1) 1098-0121 2009/01 [Refereed]
The electronic Raman scattering in overdoped (Y,Ca) Ba2 Cu3 Oy was investigated with changing hole concentration in the superconducting state. It was found that the superconducting responses such as the pair-breaking peaks in the A1g and B1g spectra and the anisotropy of the pair-breaking peak in XX and YY polarizations radically change at around the carrier doping p=0.19. Since both a - and c -axis resistivities strongly suggest the closing of pseudogap at p∼0.18, the observed change at p=0.19 in the superconducting Raman response is attributed to the electronic crossover due to the collapse of the pseudogap. © 2009 The American Physical Society. - S. Miyasaka; S. Suzuki; S. Saijo; Y. Mikasa; T. Masui; S. Tajima25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 IOP PUBLISHING LTD 150 (5) 052164-1 - 052164-4 1742-6588 2009 [Refereed]
We have investigated the transport, magnetic and thermal properties in LaFePO(1-x)F(x) to clarify the superconducting and normal state characters of this system. Above the critical temperature for superconductivity (T(c)), the low-temperature (T) resistivity is proportional to T(2), and the electronic specific heat coefficient has large value, indicating the existence of electron-electron correlation in this system. The resistive transition to the superconducting state has been broadened, as the applied magnetic field is increased. This resistive broadening is characteristic of the superconductivity in the two-dimensional electron systems such as high-T(c) cuprates. - Takahiko Masui; Kazutaka Nishikawa; Takayuki Hiramachi; Setsuko Tajima; Hiroshi Eisaki; Hijiri Kito; Akira Iyo25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 IOP PUBLISHING LTD 150 (5) 052153-1 - 052153-4 1742-6588 2009 [Refereed]
In the superconducting state of cuprates we have measured electronic Raman spectra (ERS) and plotted the pair breaking energy as a function of hole concentration in overdoped regime. The target materials in this study are Ca-substituted YBCO and Tl2201, both of which have similar T-c when it is optimally doped but different number of CuO2 planes in the unit cell. For both materials pair breaking peak energy (E-b) shows decrease with increasing carrier concentration. Interestingly E-b seems to show a rapid drop at a certain carrier concentration, where several measurements suggest the signature of quantum critical point. The similarity of the ERS between the two materials indicates that the behavior is not affected by the number of CuO2 planes in a unit cell, and that electronic state of cuprates may have a remarkable change at the critical hole concentration. - Takahiko Masui; Yuta Uraike; Kouta Nagasao; Setsuko Tajima25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 IOP PUBLISHING LTD 150 (5) 052152-1 - 052152-4 1742-6588 2009 [Refereed]
Zn and Ca substitution effects in YBa2Cu3O7-delta single crystals are presented, focusing on the anisotropy in overdoped regime. Overdoping by Ca substitution lowers the pseudogap temperature T*, and T* vanishes for heavily overdoped samples. The effect of oxygen deficiency by Ca-substitution is negligible. Zn substitution effect on residual part of c-axis resistivity is hardly observed, which is in contrast to the steady increase for in-plane resistivities. - T. Masui; T. Hiramachi; K. Nagasao; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 79 (1) 014511-1 - 014511-6 2469-9950 2009/01 [Refereed]
The electronic Raman scattering in overdoped (Y,Ca)Ba2Cu3Oy was investigated with changing hole concentration in the superconducting state. It was found that the superconducting responses such as the pair-breaking peaks in the A(1g) and B-1g spectra and the anisotropy of the pair-breaking peak in XX and YY polarizations radically change at around the carrier doping p=0.19. Since both a- and c-axis resistivities strongly suggest the closing of pseudogap at p similar to 0.18, the observed change at p=0.19 in the superconducting Raman response is attributed to the electronic crossover due to the collapse of the pseudogap. - K. Ishii; M. Hoesch; T. Inami; K. Kuzushita; K. Ohwada; M. Tsubota; Y. Murakami; J. Mizuki; Y. Endoh; K. Tsutsui; T. Tohyama; S. Maekawa; K. Yamada; T. Masui; S. Tajima; H. Kawashima; J. AkimitsuJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS PERGAMON-ELSEVIER SCIENCE LTD 69 (12) 3118 - 3124 0022-3697 2008/12 [Refereed]
We report a Cu K-edge resonant inelastic X-ray scattering (RIXS) study of high-T-c cuprates. Momentum-resolved charge excitations in the CuO2 plane are examined from parent Mott insulators to carrier-doped superconductors. The Mott gap excitation in undoped insulators is found to commonly show a larger dispersion along the [pi, pi] direction than the [pi, 0] direction. On the other hand, the resonance condition displays material dependence. The Mott gap persists in carrier-doped states. Upon hole doping, the dispersion of the Mott gap excitation becomes weaker associated with the reduction of antiferromagnetic Correlation and an intraband excitation appears as a continuum intensity below the gap at the same time. In the case of electron doping, the Mott gap excitation is prominent at the zone center and a dispersive intraband excitation is observed at finite momentum transfer. (C) 2008 Elsevier Ltd. All rights reserved. - Alfred Q. R. Baron; John P. Sutter; Satoshi Tsutsui; Hiroshi Uchiyama; Takahiko Masui; Setsuko Tajima; Rolf Heid; Klaus-Peter BohnenJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS PERGAMON-ELSEVIER SCIENCE LTD 69 (12) 3100 - 3102 0022-3697 2008/12 [Refereed]
We have measured the buckling, B-1g, phonon mode of optimally doped, de-twinned, YBa2Cu3O7-delta using inelastic X-ray scattering (IXS) at BL35XU of SPring-8. Measurements of this mode, which has atomic motion transverse to the Cu-O planes, serve to demonstrate some of the advantages of the unique two-dimensional (2-D) analyzer array at BL35. Analysis based on fitting the entire spectra simultaneously at 10 and 100 K shows that the buckling mode is rather broad in the middle of the zone (near (0.3 0 0)). We see a consistent softening of the mode at 10K as compared to 100K for all measured wave-vectors (h 0 0), and a q-dependent softening as zone center is approached. (C) 2008 Elsevier Ltd. All rights reserved. - K. Nishikawa; T. Masui; S. Tajima; H. Eisaki; H. Kito; A. IyoJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS PERGAMON-ELSEVIER SCIENCE LTD 69 (12) 3074 - 3077 0022-3697 2008/12 [Refereed]
We report Raman scattering spectra for single crystals of overdoped Tl2Ba2CuO6+delta (Tl-2201) at low temperatures. It was observed that the pair-breaking peaks in A(1g) and B-1g spectra radically shift to lower energy with carrier doping. We interpret it as s-wave component mixing into d-wave, although the crystal structure is tetragonal. Since similar phenomena were observed also in YBa2Cu3Oy and Bi2Sr2CaCu2Oz, we conclude that s-wave mixing is a common property for overdoped high-T-c superconductors. (C) 2008 Published by Elsevier Ltd. - H. Iwasawa; J. F. Douglas; K. Sato; T. Masui; Y. Yoshida; Z. Sun; H. Eisaki; H. Bando; A. Ino; M. Arita; K. Shimada; H. Namatame; M. Taniguchi; S. Tajima; S. Uchida; T. Saitoh; D. S. Dessau; Y. AiuraPHYSICAL REVIEW LETTERS AMER PHYSICAL SOC 101 (15) 157005-1 - 157005-4 0031-9007 2008/10 [Refereed]
Angle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi2Sr2CaCu2O8+delta reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, and are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches. - D. Reznik; J. -P. Ismer; I. Eremin; L. Pintschovius; T. Wolf; M. Arai; Y. Endoh; T. Masui; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 78 (13) 132503-1 - 132503-4 1098-0121 2008/10 [Refereed]
We present results of neutron scattering experiments on YBa(2)Cu(3)O(6.95) (YBCO) (T(c)=93 K). Our results indicate that magnetic collective modes due to correlated local moments are present both above and below T(c) in optimally doped YBCO. The magnon-like modes are robust and not overdamped by itinerant particle-hole excitations. We compare the experimental results to predictions of the Fermi-liquid (FL) theory in the random phase approximation. - D. Reznik; L. Pintschovius; J. M. Tranquada; M. Arai; Y. Endoh; T. Masui; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 78 (9) 1098-0121 2008/09 [Refereed]
We report the results of a detailed inelastic neutron-scattering study of renormalization of the bond-stretching phonons in optimally doped YBa2 Cu3 O6+x (YBCO). In agreement with previous work, this renormalization is strongest halfway to the zone boundary in the [010] direction where it manifests itself as a transfer of phonon spectral weight from ∼60 to ∼50 meV. Phonon renormalization begins on cooling from well above the superconducting transition temperature, Tc, but strongly accelerates at Tc. In contrast with the La2-x Srx CuO4 system, where a similar longitudinal phonon anomaly occurs, the anomaly in YBCO appears to extend in the transverse direction along the branch that connects the longitudinal mode at the in-plane wave vector qin = (0,0.25) and the transverse bond-stretching mode at qin = (0.25,0.25). Therefore, phonon renormalization in YBa2 Cu3 O6.95 seems to be consistent with a quasi-one-dimensional behavior. © 2008 The American Physical Society. - K. Nagasao; T. Masui; S. TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 468 (15-20) 1188 - 1191 0921-4534 2008/09 [Refereed]
Electronic anisotropy was studied for overdoped (Y, Ca)Ba2Cu3O7-delta with various doping levels (p). It was found that the pseudogap-like behavior in the resistivity disappear when p exceeds 0.17, independent of the oxygen deficiency. The anisotropy ratio gamma estimated from upper critical fields showed a rapid decrease at around p = 0.18, approaching gamma = 3 for p > 0.20. (C) 2008 Elsevier B.V. All rights reserved. - D. Reznik; L. Pintschovius; J. M. Tranquada; M. Arai; Y. Endoh; T. Masui; S. TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 78 (9) 094507-1 - 094507-7 2469-9950 2008/09 [Refereed]
We report the results of a detailed inelastic neutron-scattering study of renormalization of the bond-stretching phonons in optimally doped YBa2Cu3O6+x (YBCO). In agreement with previous work, this renormalization is strongest halfway to the zone boundary in the [010] direction where it manifests itself as a transfer of phonon spectral weight from similar to 60 to similar to 50 meV. Phonon renormalization begins on cooling from well above the superconducting transition temperature, T-c, but strongly accelerates at T-c. In contrast with the La2-xSrxCuO4 system, where a similar longitudinal phonon anomaly occurs, the anomaly in YBCO appears to extend in the transverse direction along the branch that connects the longitudinal mode at the in-plane wave vector q(in)= (0, 0.25) and the transverse bond-stretching mode at q(in)= (0.25, 0.25). Therefore, phonon renormalization in YBa2Cu3O6.95 seems to be consistent with a quasi-one-dimensional behavior. - Takahiko Masui; Naoki Suemitsu; Yuji Mikasa; Sergey Lee; Setsuko TajimaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN PHYSICAL SOC JAPAN 77 (7) 074720-1 - 074720-5 0031-9015 2008/07 [Refereed]
Mn substitution effects on normal and superconducting state of MgB2 are reported. Although the superconducting transition temperature (T-c) radically decreases with Mn substitution, the E-2g phonon peak in Raman spectra shows no significant change, confirming that the T-c-suppression is not due to weakening of electron-phonon coupling by band-filling but due to the pair-breaking caused by magnetic scattering. In-plane resistivity indicates that Mn substitution introduces potential scattering, which is much stronger than the case of C and Al substitution. Nevertheless, the upper critical field H-c2 is never enhanced by Mn-substitution. Based on this fact together with the behavior of H-c2 anisotropy ratio, it is likely that strong potential scattering is introduced mainly in the pi-bands. The effect of spin flip scattering other than the T-c suppression is not obvious. - R. Khasanov; S. Straessle; D. Di Castro; T. Masui; S. Miyasaka; S. Tajima; A. Bussmann-Holder; H. KellerPHYSICAL REVIEW LETTERS AMER PHYSICAL SOC 99 (23) 237601-1 - 237601-4 0031-9007 2007/12 [Refereed]
The temperature dependence of the London penetration depth lambda was measured for an untwinned single crystal of YBa(2)Cu(3)O(7-delta) along the three principal crystallographic directions (a, b, and c). Both in-plane components (lambda(-2)(a) and lambda(-2)(b)) show an inflection point in their temperature dependence which is absent in the component along the c direction (lambda(-2)(c)). The data provide convincing evidence that the in-plane superconducting order parameter is a mixture of (s+d)-wave symmetry whereas it is mainly s wave along the c direction. In conjunction with previous results it is concluded that coupled s+d-order parameters are universal and intrinsic to cuprate superconductors. - T. Hiramachi; T. Masui; S. TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 463 89 - 92 0921-4534 2007/10 [Refereed]
We measured Raman spectra of a series of Ca-substituted and oxygen- controlled YBCO single crystals at low temperatures. It was found that the change of pair-breaking peak energy and intensity of A(1g) and B-1g were explained with carrier concentration rather than orthorhombic lattice distortion. (C) 2007 Elsevier B.V. All rights reserved. - H. Iwasawa; Y. Aiura; T. Saitoh; H. Eisaki; H. Bando; A. Ino; M. Arita; K. Shimada; H. Namatame; M. Taniguchi; T. Masui; S. Tajima; M. Ishikado; K. Fujita; S. Uchida; J. F. Douglas; Z. Sun; D. S. DessauPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 463 52 - 55 0921-4534 2007/10 [Refereed]
We have re-examined the oxygen isotope effect in high-temperature superconductors Bi2Sr2CaCu2O8+delta using high-precision angle-resolved photoemission spectroscopy with low-energy photons in order to elucidate the origin of the kink. The results taken with a much improved energy and momentum resolution showed the absence of the reported unusual oxygen isotope effect. (C) 2007 Elsevier B.V. All rights reserved. - S. Tajima; T. Masui; N. Suemitsu; S. Lee; T. KakeshitaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 460 (Part 1) 74 - 77 0921-4534 2007/09 [Refereed]
We have studied the effects of G and Mn-substitution on physical properties of MgB2, using single crystals. Optical reflectivity measurements have successfully separated the changes in plasma frequency and scattering rate in sigma- and pi-band. The former indicates that electrons are doped by C-substitution but the two dimensional sigma-band Fermi surfaces survive at least up to 10% doping. Increase in carrier scattering rate with C-substitution is much stronger in the sigma-bands than in the pi-bands, which leads to the decrease in the in-plane coherence length as well as the anisotropy of H-c2. Raman scattering experiment showed that Mn impurity acts as a strong magnetic pair-breaker without changing the electron-phonon coupling. (c) 2007 Elsevier B.V. All rights reserved. - T. MasuiPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 456 (1-2) 102 - 107 0921-4534 2007/06 [Refereed][Invited]
Recent advances in the study of MgB2 are reviewed, with focus on the transport properties and Raman scattering measurements for impurity substituted crystals. Carbon and Aluminium substitution change band filling, introduce intraband and interband scattering. These effects are seen in the temperature dependence of resistivity, Hall coefficients, and phonon peak of Raman spectra. Manganese substitution introduces magnetic scattering, that increases resistivity but gives little change in Raman spectra. The effect of disorder in neutron irradiated samples is also discussed, (c) 2007 Elsevier B.V. All rights reserved. - John F. Douglas; Hideaki Iwasawa; Zhe Sun; Alexei V. Fedorov; Motoyuki Ishikado; Tomohiko Saitoh; Hiroshi Eisaki; Hiroshi Bando; Takeshi Iwase; Akihiro Ino; Masashi Arita; Kenya Shimada; Hirofumi Namatame; Masaki Taniguchi; Takahiko Masui; Setsuko Tajima; Kazuhiro Fujita; Shin-ichi Uchida; Yoshihiro Aiura; Daniel S. DessauNATURE NATURE PUBLISHING GROUP 446 (7133) E5 - E5 0028-0836 2007/03 [Refereed]
- N. Suemitsu; T. Masui; S. Lee; S. TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 445 39 - 41 0921-4534 2006/10 [Refereed]
We have prepared Mn substituted MgB2 single crystals and measured their physical properties. The transition temperature (T-c) steeply decreased with increasing Mn content. In the Raman spectrum, the E-2g-phonon frequency hardly shifted from that of parent MgB2, in sharp contrast to the case of Al/C substitution. This implies that the mechanisms of Tc suppression are different between Al/C substitution and Mn substitution. (c) 2006 Published by Elsevier B.V. - Jinho Lee; K. Fujita; K. McElroy; J. A. Slezak; M. Wang; Y. Aiura; H. Bando; M. Ishikado; T. Masui; J. -X. Zhu; A. V. Balatsky; H. Eisaki; S. Uchida; J. C. DavisNATURE NATURE PUBLISHING GROUP 442 (7102) 546 - 550 0028-0836 2006/08 [Refereed]
Formation of electron pairs is essential to superconductivity. For conventional superconductors, tunnelling spectroscopy has established that pairing is mediated by bosonic modes (phonons); a peak in the second derivative of tunnel current d(2)I/dV(2) corresponds to each phonon mode(1-3). For high-transition-temperature (high-T-c) superconductivity, however, no boson mediating electron pairing has been identified. One explanation could be that electron pair formation(4) and related electron - boson interactions are heterogeneous at the atomic scale and therefore challenging to characterize. However, with the latest advances in d(2)I/dV(2) spectroscopy using scanning tunnelling microscopy, it has become possible to study bosonic modes directly at the atomic scale(5). Here we report d(2)I/dV(2) imaging(6-8) studies of the high-T-c superconductor Bi2Sr2CaCu2O8+delta. We find intense disorder of electron - boson interaction energies at the nanometre scale, along with the expected modulations in d(2) I/dV(2) ( refs 9, 10). Changing the density of holes has minimal effects on both the average mode energies and the modulations, indicating that the bosonic modes are unrelated to electronic or magnetic structure. Instead, the modes appear to be local lattice vibrations, as substitution of O-18 for O-16 throughout the material reduces the average mode energy by approximately 6 per cent - the expected effect of this isotope substitution on lattice vibration frequencies(5). Significantly, the mode energies are always spatially anticorrelated with the superconducting pairing-gap energies, suggesting an interplay between these lattice vibration modes and the superconductivity. - R Lortz; T Tomita; Y Wang; A Junod; JS Schilling; T Masui; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 434 (2) 194 - 198 0921-4534 2006/02 [Refereed]
The superconducting transition in a single overdoped, detwinned YBa2Cu3Ox (YBCO) crystal is studied using four different probes. Whereas the AC and DC magnetic susceptibilities find a dominant transition at 88 K with a smaller effect near 92 K, the specific heat and electrical resistivity reveal only a single transition at 88 K and 92 K, respectively. Under hydrostatic pressures to 0.60 GPa these two transitions shift in opposite directions, their separation increasing. The present experiments clearly show that the bulk transition lies at 88 K and originates from fully oxygenated YBCO; the 92 K transition likely arises from filamentary superconductivity in a minority optimally doped phase (< 1%) of YBCO located at or near the crystal surface. (c) 2005 Elsevier B.V. All rights reserved. - T. Kakeshita; T. Masui; S. TajimaLOW TEMPERATURE PHYSICS, PTS A AND B AMER INST PHYSICS 850 (1) 449 - + 0094-243X 2006 [Refereed]
We report on superfluid density estimated from optical spectra of YBa2Cu3O7-delta(YBCO). Some recent reports have suggested that optical measurements generally underestimate the superfluid density compared to mu SR. We discuss the origin of the suppression of the superfluid density with nano-scale inhomogeneous picture on CuO2 plane. - K. Ishii; K. Tsutsui; Y. Endoh; T. Tohyama; K. Kuzushita; T. Inami; K. Ohwada; S. Maekawa; T. Masui; S. Tajima; Y. Murakami; J. MizukiLOW TEMPERATURE PHYSICS, PTS A AND B AMER INST PHYSICS 850 (1) 445 - + 0094-243X 2006 [Refereed]
Momentum dependence of Mott gap excitations in the twin-free YBa(2)Cu(3)3O(7-delta) at optimal doping has been studied by the resonant inelastic x-ray scattering at the Cu K-edge. We have succeeded to distinguish between the excitations from CuO chain and that from the CuO2 plane. The excitation from the chain is enhanced at 2 eV near the zone boundary of the b* direction, while the excitation from the plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard models reproduces these features when we assume a smaller value of on-site Coulomb repulsion of the chain site than that of the plane site. - D Reznik; L Pintschovius; Y Endoh; P Bourges; Y Sidis; T Masui; S TajimaJOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS PERGAMON-ELSEVIER SCIENCE LTD 67 (1-3) 509 - 510 0022-3697 2006/01 [Refereed]
Spin gap in optimally-doped YBCO was investigated by inelastic neutron scattering. We found that q-integrated spectral weight in the vicinity of the spin gap has a shape of a step function at 10 K with the sharp resolution-limited onset at 33 meV, i.e. there is no observable spectral weight at 31 meV but full spectral weight at 35 meV. The spin gap does not soften or 'fill in' as the temperature is increased to T-c. Above T-c we find no evidence for q-dependent magnetic signal at 35 meV. (c) 2005 Elsevier Ltd. All rights reserved. - T Masui; M Limonov; H Uchiyama; S Tajima; A YamanakaPHYSICAL REVIEW LETTERS AMERICAN PHYSICAL SOC 95 (20) 207001-1 - 207001-4 0031-9007 2005/11 [Refereed]
We found a strong X-Y anisotropy of the pair-breaking peak in the Raman scattering of heavily overdoped (Y,Ca)Ba2Cu3O7-delta (T-c=65 K). The pair-breaking peak is radically suppressed in the YY-polarized spectrum. We ascribe this anomaly to the effect of quantum interference between the Raman processes of the CuO-chain and the CuO2-plane electronic excitations that might take place as a result of the increase in the transfer matrix due to overdoping. - T Kakeshita; T Masui; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 426 (Part 1) 184 - 188 0921-4534 2005/10 [Refereed]
We report on the in-plane optical spectra in underdoped YBa2Cu3O7 (YBCO) using a twin-free single crystal. At low temperatures, there exist two components in the optical conductivity which are considered as a Drude term by quasiparticles in a nodal direction and the pseudogap excitation in an antinodal direction. A large residual conductivity together with pseudogap, feature is consistent with the picture of inhomogeneous in-plane electronic state observed by scanning tunneling microscopy (STM). We estimate a superfluid density n(s) from optical spectra and discuss a universal relation between T-c and n(s). The value estimated from our results is considerably smaller than that of the mu SR measurement. It is considered due to the inhomogeneity of in-plane, the difference of applying field, and a property on pseudogap. (c) 2005 Elsevier B.V. All rights reserved. - T Masui; E Ohmichi; S Tajima; T OsadaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 426 (Part 1) 335 - 339 0921-4534 2005/10 [Refereed]
The irreversibility fields of Ca-YBCO single crystals are estimated from torque measurement and dc-resistivity. The small anisotropy about 3 is related to the heavy overdoping with help of Ca-substitution. For the optimally doped Ca-YBCO, the irreversibility field is lower than that for the Ca-free YBCO, when compared at a fixed TIT, Since the former has more oxygen deficiencies, this result contradicts with the general understanding that CuO-chain deficiency is considered to enhance vortex pinning. The resistivity in magnetic fields shows that fluctuation effect is largely suppressed for heavily overdoped Ca-YBCO. (c) 2005 Elsevier B.V. All rights reserved. - AT Savici; A Fukaya; IM Gat-Malureanu; T Ito; PL Russo; YJ Uemura; CR Wiebe; PP Kyriakou; GJ MacDougall; MT Rovers; GM Luke; KM Kojima; M Goto; S Uchida; R Kadono; K Yamada; S Tajima; T Masui; H Eisaki; N Kaneko; M Greven; GD GuPHYSICAL REVIEW LETTERS AMERICAN PHYSICAL SOC 95 (15) 157001-1 - 157001-4 0031-9007 2005/10 [Refereed]
Muon spin relaxation measurements in high transverse magnetic fields (parallel to c<^>) revealed strong field-induced quasistatic magnetism in the underdoped and Eu-doped (La,Sr)(2)CuO4 and La1.875Ba0.125CuO4, existing well above T-c and T-N. The susceptibility counterpart of Cu spin polarization, derived from the muon spin relaxation rate, exhibits a divergent behavior towards T similar to 25 K. No field-induced magnetism was detected in overdoped La1.81Sr0.19CuO4, optimally doped Bi2212, and Zn-doped YBa2Cu3O7. - R Lortz; A Junod; D Jaccard; YX Wang; C Meingast; T Masui; S TajimaJOURNAL OF PHYSICS-CONDENSED MATTER IOP PUBLISHING LTD 17 (26) 4135 - 4145 0953-8984 2005/07 [Refereed]
The evolution of the specific-heat anomaly in the overdoped range of a single crystal of the high-temperature superconductor YBa2Cu3O7 has been studied under the influence of pressure up to 10 GPa, using AC calorimetry in a Bridgman-type pressure cell. We show that the specific-heat jump as well as the bulk T-c are reduced with increasing pressure in accordance with a simple charge-transfer model. This new method enables us through pressure-induced charge transfer to study the doping dependence of the superconducting transition, as well as the evolution of the superconducting condensation energy on a single stoichiometric sample without adding atomic disorder. - K Ishii; K Tsutsui; Y Endoh; T Tohyama; K Kuzushita; T Inami; K Ohwada; S Maekawa; T Masui; S Tajima; Y Murakami; J MizukiPHYSICAL REVIEW LETTERS AMER PHYSICAL SOC 94 (18) 187002-1 - 187002-4 0031-9007 2005/05 [Refereed]
Mott gap excitations in the optimally doped high-T-c superconductor YBa2Cu3O7-delta (T-c=93 K) have been studied by the resonant inelastic x-ray scattering method. Anisotropic spectra in the ab plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the b* direction, while the excitation from the CuO2 plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculations based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO2 plane site. - M. Beleggia; G. Pozzi; A. Tonomura; H. Kasai; T. Matsuda; K. Harada; T. Akashi; T. Masui; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 70 (18) 1 - 8 0163-1829 2004/11 [Refereed]
More realistic simulations of the magnetic field and electron optical phase shift associated to pancake vortices in layered high-Tc superconducting specimen require a number of layers larger than 7, the practical upper limit set by the discrete algebraic approach followed so far. This goal can be achieved by resorting to a continuum approximation of the screening layers above and below the one containing the pancake vortex. It is thus possible to increase the number of layers and to investigate more exotic vortex core structures than those represented by the pancakes pinned at tilted columnar defects. In particular it will be shown how recently observed dumbbell-like contrast features in the out-of-focus images of superconducting vortices forming a large angle with the specimen surfaces can be interpreted as due to a kinked structure of the pancakes. - E. Ohmichi; E. Komatsu; T. Masui; S. Lee; S. Tajima; T. OsadaPhysical Review B - Condensed Matter and Materials Physics 70 (17) 1 - 5 0163-1829 2004/11 [Refereed]
We have investigated the carbon substitution effect on the peak effect of MgB2 single crystals. The peak effect originates from the order-disorder transition of vortices, so that disorders introduced by carbon substitution are expected to have strong influence on the vortex phase diagram. In fact, a systematic study of the rf penetration depth λrf has revealed that the order-disorder transition line monotonously shifts to the low-field region with carbon content in H∥ab and c. The results are discussed in terms of the effect of weak point disorder on the vortex order-disorder transition. - D Reznik; P Bourges; L Pintschovius; Y Endoh; Y Sidis; T Masui; S TajimaPHYSICAL REVIEW LETTERS AMERICAN PHYSICAL SOC 93 (20) 207003-1 - 207003-4 0031-9007 2004/11 [Refereed]
Detailed neutron scattering measurements of YBa2Cu3O6.95 found that the resonance peak and incommensurate magnetic scattering induced by superconductivity represent the same physical phenomenon: two dispersive branches that converge near 41 meV and the in-plane wave vector q(AF)=(pi/a,pi/a) to form the resonance peak. One branch has a circular symmetry around q(AF) and quadratic downward dispersion from approximate to41 meV to the spin gap of 33+/-1 meV. The other, of lower intensity, disperses from approximate to41 meV to at least 55 meV. Our results exclude a quartet of vertical incommensurate rods in q-omega space expected from spin waves produced by dynamical charge stripes as an origin of the observed incommensurate scattering in optimally doped YBCO. - M Beleggia; G Pozzi; A Tonomura; H Kasai; T Matsuda; K Harada; T Akashi; T Masui; S TajimaPHYSICAL REVIEW B AMERICAN PHYSICAL SOC 70 (18) 184518-1 - 184518-8 1098-0121 2004/11 [Refereed]
More realistic simulations of the magnetic field and electron optical phase shift associated to pancake vortices in layered high-T-c superconducting specimen require a number of layers larger than 7, the practical upper limit set by the discrete algebraic approach followed so far. This goal can be achieved by resorting to a continuum approximation of the screening layers above and below the one containing the pancake vortex. It is thus possible to increase the number of layers and to investigate more exotic vortex core structures than those represented by the pancakes pinned at tilted columnar defects. In particular it will be shown how recently observed dumbbell-like contrast features in the out-of-focus images of superconducting vortices forming a large angle with the specimen surfaces can be interpreted as due to a kinked structure of the pancakes. - E Ohmichi; E Komatsu; T Masui; S Lee; S Tajima; T OsadaPHYSICAL REVIEW B AMER PHYSICAL SOC 70 (17) 174513-1 - 174513-5 2469-9950 2004/11 [Refereed]
We have investigated the carbon substitution effect on the peak effect of MgB2 single crystals. The peak effect originates from the order-disorder transition of vortices, so that disorders introduced by carbon substitution are expected to have strong influence on the vortex phase diagram. In fact, a systematic study of the rf penetration depth lambda(rf) has revealed that the order-disorder transition line monotonously shifts to the low-field region with carbon content in Hparallel toab and c. The results are discussed in terms of the effect of weak point disorder on the vortex order-disorder transition. - T Masui; S Lee; A Yamamoto; H Uchiyama; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 412 (Part 1) 303 - 306 0921-4534 2004/10 [Refereed]
The superconducting properties of carbon-substituted MgB2 single crystals are studied. We found that C-substitution modifies superconducting properties such as anisotropy and irreversibility field. The highest H-c2 can be achieved by the C-substitution around 3-5% per B-atom. In the superconductivity transition, the resistivity is almost ohmic; this is remarkable contrast to the case of C-free crystals. (C) 2004 Elsevier B.V. All rights reserved. - T Masui; Y Takano; K Yoshida; K Kajita; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 412 (Part 1) 515 - 520 0921-4534 2004/10 [Refereed]
We measured magnetization of Zn-substituted YBCO single crystals in the overdoped, optimally-doped, and underdoped regimes, and estimated critical current density (J(c)). The Zn-substitution less than 1% enhances the second peak of J(c) in overdoped regime, while it almost suppresses in underdoped regime. The optimized Zn-concentration changes as function of carrier concentration. Carrier-doping increases irreversibility field (H-irr), while Zn-substitution decreases H-irr at all doping levels. It implies that the point defect is not effective pinning center for higher H-irr. (C) 2004 Elsevier B.V. All rights reserved. - L Pintschovius; Y Endoh; D Reznik; H Hiraka; J Tranquada; W Reichardt; P Bourges; Y Sidis; H Uchiyama; T Masui; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 412 (Part 1) 70 - 75 0921-4534 2004/10 [Refereed]
Inelastic neutron scattering investigations on optimally doped YBCO revealed a very pronounced temperature dependence of the Cu-O in-plane bond-stretching vibrations along the (0 1 0)-direction: a downward shift of spectral weight with decreasing temperature by at least 10 meV in a narrow range of wave vectors halfway to the zone boundary. The temperature evolution starts around 200 K, well above the superconducting transition temperature. This phonon anomaly provides strong evidence for large electron-phonon coupling. It also indicates an incipient charge density wave instability within the CuO2 planes reminiscent of dynamical charge stripes. The magnetic fluctuations have been investigated in great detail on the same sample. Incommensurate spin fluctuations have been observed for energies both below and above the energy of the resonance peak at E = 41 meV. However, the dispersive nature of these fluctuations as well as their apparent isotropy in the basal plane speak against an interpretation of the spin fluctuation spectrum in the framework of the classical stripe phase picture. (C) 2004 Elsevier B.V. All rights reserved. - S Lee; T Masui; A Yamamoto; H Uchiyama; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 412 (Part 1) 31 - 35 0921-4534 2004/10 [Refereed]
Here, we discuss the possibility of accidental C-doping of MgB2 crystals and inhomogeneous C distribution of Mg(B1-xCx)(2) single crystals with x = 0.02-0.125 grown under high pressure. Structure refinement was performed on the heavily C-doped crystal with x = 0.125 which has confirmed no evidence of microscopic phase separation. Resistivity and magnetization measurements were also preformed on several of as-grown and post-annealed crystals with a inhomogeneous C distribution. (C) 2004 Elsevier B.V. All rights reserved. - E Ohmichi; T Masui; S Lee; S Tajima; T OsadaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN PHYSICAL SOC JAPAN 73 (8) 2065 - 2068 0031-9015 2004/08 [Refereed]
We report on a detailed study of the irreversibility field H-irr of single crystals of Mg(B1-xCx)(2) (x = 0, 2, 3.5, 5 and 7.5%) in strong magnetic fields of up to 40 T. Highly sensitive torque measurements revealed that H-irr, is greatly enhanced by a factor of two (mu(0)H(irr)(0) similar or equal to 33 T with x = 5%) by carbon substitution compared with that of the pristine MgB2, owing to a reduction in in-plane coherence length. We also observed the temperature-dependent H-irr anisotropy for all carbon contents. This strongly suggests that the two-gap superconductivity of MgB2 is less influenced by a small amount of carbon substitution. We discuss these results by focusing on the impact of carrier doping and impurity scattering on a two-gap superconductor. - T. Masui; S. Lee; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 70 (2) 1 - 24504 0163-1829 2004/07 [Refereed]
The electronic properties of the carbon-substituted MgB2 single crystals are reported. The carbon substitution drops Tc below 2 K. In-plane resistivity shows a remarkable increase in residual resistivity by C substitution, while the change of in-plane/out-of-plane Hall coefficients is rather small. Raman scattering spectra indicate that the E2g-phonon frequency radically hardens with increasing the carbon content, suggesting the weakening of electron-phonon coupling. Another striking C effect is the increases of the second critical fields in both in-plane and out-of-plane directions, accompanied by a reduction in the anisotropy ratio. The possible changes in the electronic state and the origin of Tc suppression by C substitution are discussed. - T Masui; S Lee; S TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 70 (2) 024504-1 - 024504-7 1098-0121 2004/07 [Refereed]
The electronic properties of the carbon-substituted MgB2 single crystals are reported. The carbon substitution drops T-c below 2 K. In-plane resistivity shows a remarkable increase in residual resistivity by C substitution, while the change of in-plane/out-of-plane Hall coefficients is rather small. Raman scattering spectra indicate that the E-2g-phonon frequency radically hardens with increasing the carbon content, suggesting the weakening of electron-phonon coupling. Another striking C effect is the increases of the second critical fields in both in-plane and out-of-plane directions, accompanied by a reduction in the anisotropy ratio. The possible changes in the electronic state and the origin of T-c suppression by C substitution are discussed. - L. Pintschovius; D. Reznik; W. Reichardt; Y. Endoh; H. Hiraka; J. M. Tranquada; H. Uchiyama; T. Masui; S. TajimaPhysical Review B - Condensed Matter and Materials Physics 69 (21) 1 - 214506 0163-1829 2004/06 [Refereed]
We report results of inelastic neutron scattering measurements of phonon dispersions in optimally doped YBa2Cu3O6.95 and compare them with model calculations. The focus is on the in-plane oxygen bond-stretching phonon branches. The study of these modes is complicated by anticrossings with c-axis-polarized branches such effects are interpreted through lattice-dynamical shell-model calculations. The in-plane anisotropy of the bond-stretching phonons was firmly ascertained from measurements on a detwinned sample. Studying not only the in-plane modes involving in-phase motion for the two Cu-O layers within a unit cell but also those with opposite-phase motion was of great help for establishing a clear experimental picture. The measurements confirm that the in-plane oxygen bond-stretching phonon branches disperse steeply downwards from the zone center in both the a and the b directions indicating a strong electron-phonon coupling. For the b-axis-polarized bond-stretching phonons, there is an additional feature of considerable interest: a sharp local frequency minimum was found to develop on cooling from room temperature to T = 10 K at wave vector q≈0.27 r.l.u. - L Pintschovius; D Reznik; W Reichardt; Y Endoh; H Hiraka; JM Tranquada; H Uchiyama; T Masui; S TajimaPHYSICAL REVIEW B AMER PHYSICAL SOC 69 (21) 214506-1 - 214506-11 2469-9950 2004/06 [Refereed]
We report results of inelastic neutron scattering measurements of phonon dispersions in optimally doped YBa2Cu3O6.95 and compare them with model calculations. The focus is on the in-plane oxygen bond-stretching phonon branches. The study of these modes is complicated by anticrossings with c-axis-polarized branches; such effects are interpreted through lattice-dynamical shell-model calculations. The in-plane anisotropy of the bond-stretching phonons was firmly ascertained from measurements on a detwinned sample. Studying not only the in-plane modes involving in-phase motion for the two Cu-O layers within a unit cell but also those with opposite-phase motion was of great help for establishing a clear experimental picture. The measurements confirm that the in-plane oxygen bond-stretching phonon branches disperse steeply downwards from the zone center in both the a and the b directions indicating a strong electron-phonon coupling. For the b-axis-polarized bond-stretching phonons, there is an additional feature of considerable interest: a sharp local frequency minimum was found to develop on cooling from room temperature to T=10 K at wave vector qapproximate to0.27 r.l.u. - M. Limonov; S. Lee; T. Masui; H. Uchiyama; S. Tajima; A. YamanakaPhysica Status Solidi C: Conferences 1 (11) 3077 - 3080 1610-1634 2004 [Refereed]
Raman scattering spectra of (123) and Bi-based high-temperature superconductors (HTSC) with different doping levels have been investigated. It is demonstrated that phonons in HTSC can provide unique information on energy, symmetry, temperature- and doping- dependencies of the superconducting gap and pseudogap. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. - M Limonov; S Lee; T Masui; H Uchiyama; S Tajima; A YamanakaPHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL. 1, NO. 11 WILEY-V C H VERLAG GMBH 1 (11) 3077 - 3080 1862-6351 2004 [Refereed]
Raman scattering spectra of (123) and Bi-based high-temperature superconductors (HTSC) with different doping levels have been investigated. It is demonstrated that phonons in HTSC can provide unique information on energy, symmetry, temperature- and doping-dependencies of the superconducting gap and pseudogap. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheirn. - T Masui; S Lee; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 392 (Part 1) 281 - 285 0921-4534 2003/10 [Refereed]
By controlling growing process, we have succeeded in making MgB2 single crystals with different electronic properties. In the crystals with smaller c/a, larger residual resistivity ratio, higher T-c, and higher anisotropy in H-c2 are observed. In superconducting state, a difference of anisotropy is attributable to H-c2(parallel toc), suggesting a considerable change beyond the disorder effect due to lattice strain. We discuss possible origins for the changes. (C) 2003 Elsevier B.V. All rights reserved. - M Limonov; T Masui; H Uchiyama; S Lee; S Tajima; A YamanakaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 392 (Part 1) 53 - 56 0921-4534 2003/10 [Refereed]
In order to get insight into the overdoped electronic state, Raman scattering in heavily overdoped detwinned (Y,Ca)Ba2Cu3O7-delta crystals (T-c = 65 K) has been investigated. In the A(1g) and B-1g polarizations, the electronic pair-breaking peak is located at nearly the same energy of about 220 cm(-1), in contrast to the polarization dependent position of the peak in optimally doped YBa2Cu3 O7-delta crystals. The result is in favor of d + s-pairing symmetry in this overdoped material. The spectra also show the strong superconductivity induced XY-anisotropy in intensity of the pair-breaking peak, which indicates the existence of quantum interference between CuO2 planes and CuO-chains in this compound. (C) 2003 Elsevier B.V. All rights reserved. - S Lee; T Masui; A Yamamoto; H Uchiyama; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 397 (1-2) 7 - 13 0921-4534 2003/10 [Refereed]
Carbon-substituted MgB2 single crystals, Mg(B1-xCx)(2) of 0.3-1.0 mm size were grown for x = 0.02-0.15 by a high-pressure technique. The doping dependence of lattice constants studied in a range of x = 0.0-0.2 shows a monotonic decrease in a, while the c parameter remains almost invariant. Using X-ray diffraction and Auger electron spectroscopy, the solubility limit of C in MgB2 was estimated to be about 15 +/- 1%, which is substantially larger than that reported for the polycrystalline samples synthesized by encapsulation techniques. Measurements of the temperature dependence of magnetization and resistivity showed a dramatic decrease in T, with C-substitution, followed by complete suppression of superconductivity for x > 0.125. Resistivity measurements in magnetic fields parallel and perpendicular to the basal plane of the crystals showed a nearly isotropic state in the heavily doped crystals (x > 0.1). (C) 2003 Elsevier B.V. All rights reserved. - T. Masui; M. Limonov; H. Uchiyama; S. Lee; S. Tajima; A. YamanakaPhysical Review B - Condensed Matter and Materials Physics 68 (6) 1550-235X 2003/08 [Refereed]
Raman scattering in the heavily overdoped (Y, Ca)Ba2Cu3O7−δ (Tc=65 K) and Bi2Sr2CaCu2O8+δ (Tc=55 K) crystals has been investigated. For both the crystals, the electronic pair-breaking peaks in the A1g and B1g polarizations were largely shifted to the low energies close to a half of 2Δ0, Δ0 being the maximum gap. It strongly suggests s-wave mixing into the d-wave superconducting order parameter and the consequent manifestation of the Coulomb screening effect in the B1g channel. Gradual mixing of s-wave component with overdoping is not due to the change of crystal structure symmetry but a generic feature in all high-Tc superconducting cuprates. © 2003 The American Physical Society. - T Masui; M Limonov; H Uchiyama; S Lee; S Tajima; A YamanakaPHYSICAL REVIEW B AMER PHYSICAL SOC 68 (6) 060506(R)-1 - 060506(R)-4 2469-9950 2003/08 [Refereed]
Raman scattering in the heavily overdoped (Y,Ca)Ba2Cu3O7-delta (T-c=65 K) and Bi2Sr2CaCu2O8+delta (T-c=55 K) crystals has been investigated. For both the crystals, the electronic pair-breaking peaks in the A(1g) and B-1g polarizations were largely shifted to the low energies close to a half of 2Delta(0), Delta(0) being the maximum gap. It strongly suggests s-wave mixing into the d-wave superconducting order parameter and the consequent manifestation of the Coulomb screening effect in the B-1g channel. Gradual mixing of s-wave component with overdoping is not due to the change of crystal structure symmetry but a generic feature in all high-T-c superconducting cuprates. - Y Eltsev; K Nakao; S Lee; T Masui; N Chikumoto; S Tajima; N Koshizuka; M MurakamiJOURNAL OF LOW TEMPERATURE PHYSICS SPRINGER/PLENUM PUBLISHERS 131 (5-6) 1069 - 1073 0022-2291 2003/06 [Refereed]
We report on study of transport properties of MgB2 single crystals. The normal state resistivity has been found to be anisotropic with resistivity ratio rho(c)/rho(ab) = 3.5. In agreement with the results of band structure calculations the normal state Hall effect measurements with H//ab-planes and H//c-axis show two type carrier behavior. Below T-c, the in-plane as well as the out-of-plane Hall resistivity, rho(xy) and rho(zx), display no sign change anomaly. Furthermore, both rho(xy) and rho(zx) have been found to scale with corresponding longitudinal resistivity with the same exponent beta = 1.5. - D Reznik; L Pintschovius; W Reichardt; Y Endoh; H Hiraka; JM Tranquada; S Tajima; H Uchiyama; T MasuiJOURNAL OF LOW TEMPERATURE PHYSICS KLUWER ACADEMIC/PLENUM PUBL 131 (3-4) 417 - 421 0022-2291 2003/05 [Refereed]
We report results of inelastic neutron scattering measurements of phonon dispersions on a detwinned sample of YBa2Cu3O7 and compare them with model calculations. Plane oxygen bond stretching phonon branches disperse steeply downwards from the zone center in both the a and the b direction indicating a strong electron-phonon coupling. Half way to the zone boundary, the phonon peaks become ill-defined but we see no need to invoke unit cell doubling or charge stripe formation: lattice dynamical shell model calculations predict such behavior as a result of branch anticrossings. There were no observable superconductivity-related temperature effects on selected plane oxygen bond stretching modes measured on a twinned sample. - H Uchiyama; T Masui; S TajimaJOURNAL OF LOW TEMPERATURE PHYSICS SPRINGER/PLENUM PUBLISHERS 131 (3-4) 287 - 291 0022-2291 2003/05 [Refereed]
We measured angle-resolved photoemission spectra of untwinned Ca substituted YBa2Cu3O7-delta (YBCO) in the overdoped region, and compared them to those of optimally doped Ca-free YBCO. In contrast to the spectra of Ca-free YBCO, where a gap feature is not clearly seen due to the surface-derived states, the spectra of Ca substituted YBCO disclose bulk features with little effect of the surface states. At (pi, 0), a superconducting peak and a leading edge shift are clearly observed, while, at (0, pi), a strong peak remains at the Fermi energy both above and below T-c, unaccompanied by a shift due to superconductivity. - N Watanabe; T Masui; Y Itoh; T Machi; Kato, I; N Koshizuka; M MurakamiPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 388 241 - 242 0921-4534 2003/05 [Refereed]
We report the out-of-plane and in-plane magnetic susceptibility and resistivity of Ni-doped La2-xSrxCuO4 single crystals. Our data shows that in lightly Sr doped compounds the Neel temperature T-N increased with increasing Ni concentration. As the temperature is lowered, the resistivity deviates from the impurity band conduction process and becomes dominated by the variable range hopping process associated with the evolving of antiferromagnetic ordering. (C) 2003 Elsevier Science B.V. All rights reserved. - S Tajima; T Masui; J Quilty; S Lee; A Yamamoto; A YamanakaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 388 103 - 104 0921-4534 2003/05 [Refereed]
From precise analyses of resistivity data and Raman scattering spectra from MgB2 single crystals, we have extracted the electron-phonon (e-p) coupling constants and specified the relevant phonon mode and electronic bands that play a main role in the superconductivity. It has been demonstrated that the strong coupling of the E-2g. boron vibrational mode with the sigma-band holes governs the normal state conduction and the high-T-c superconductivity mechanism. The smaller gap on the pi-bands found by k-selective Raman scattering measurements is reconciled with the weak e-p coupling and large scattering rate in these bands. (C) 2003 Elsevier Science B.V. All rights reserved. - T Masui; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 385 (1-2) 91 - 97 0921-4534 2003/03 [Refereed][Invited]
The transport properties of magnesium diboride in the normal state are briefly reviewed. The temperature dependence of resistivity is explained by taking into account the contribution of E-2g optical phonon mode. From the sign of Hall coefficient, thermoelectric power, the type of predominant carriers is determined for each direction. In the Hall coefficient, the multiband effect is clearly observed, as a strong anisotropy between in-plane and out-of-plane component. In the thermoelectric power, a phonon contribution to thermal transport manifests itself. (C) 2002 Elsevier Science B.V. All rights reserved. - Sergey Lee; T. Masui; H. Mori; Yu Eltsev; A. Yamamoto; S. TajimaSuperconductor Science and Technology 16 (2) 213 - 220 0953-2048 2003/02 [Refereed]
Crystal growth and characterization of MgB2 under high pressure and temperature in the Mg-B-N system were discussed. The relation between structural and superconducting properties were also studied. Results showed that the Mg-B-N system is very promising for crystal growth of MgB2 under high pressure. - T Masui; S Lee; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 383 (4) 299 - 305 0921-4534 2003/01 [Refereed]
We report resistivity and magnetization of single crystal MgB2, focusing on the broadening of superconducting (SC) transition in magnetic fields. In-plane and out-of-plane resistivity indicate that the broadening of SC transition is independent of Lorentz force and that it is merely dependent on the magnetic field direction. In magnetization, diamagnetic signal begins to appear at almost the same temperature as the onset temperature of resistivity transition. These results suggest that the broadening is attributed not to the surface superconductivity but to the SC fluctuation or the vortex-liquid picture, owing to the short coherence length and the high transition temperature of MgB2. (C) 2002 Elsevier Science B.V. All rights reserved. - A Yamamoto; C Takao; T Masui; M Izumi; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 383 (3) 197 - 206 0921-4534 2002/12 [Refereed]
Superconductivity with T-c above 9 K was found in metal-deficient NbB2 prepared under 5 GPa, while no clear superconductivity was observed down to 3 K in stoichiometric NbB2. The superconductivity was observed above x = 0.04 in Nb1-xB2, and the lattice parameters also changed abruptly at x = 0.04. As x increased, the transition temperature T-c slightly rose and fell with the maximum value of 9.2 K at x = 0.24 for the samples sintered at 5 GPa and 1200 degreesC. The T-c-value changed in the range from 7 to 9 K, depending on the sintering pressure. A series of Ta1-xB2 (0 less than or equal to x less than or equal to 0.24) was also synthesized under high pressure to examine a special effect of high-pressure synthesis. (C) 2002 Elsevier Science B.V. All rights reserved. - Y Eltsev; K Nakao; S Lee; T Masui; N Chikumoto; S Tajima; N Koshizuka; M MurakamiPHYSICAL REVIEW B AMER PHYSICAL SOC 66 (18) 180504(R)-1 - 180504(R)-4 1098-0121 2002/11 [Refereed]
We report resistivity and the Hall-effect measurements in the normal and superconducting states of MgB2 single crystals. The resistivity has been found to be anisotropic with slightly temperature-dependent resistivity ratio of about 3.5. The Hall constant, with a magnetic field parallel to the Mg and B sheets, is negative in contrast to the holelike Hall response with a field directed along the c axis, indicating presence of both types of charge carriers and, thus, the multiband electronic structure of MgB2. The Hall effect in the mixed state shows no sign change anomaly, reproducing Hall-effect behavior in clean limit type-II superconductors. - N Watanabe; T Masui; Y Itoh; Kato, I; T Machi; N Koshizuka; M MurakamiJOURNAL OF SUPERCONDUCTIVITY SPRINGER/PLENUM PUBLISHERS 15 (5) 451 - 454 0896-1107 2002/10 [Refereed]
We report the out-of-plane and in-plane magnetic susceptibility and resistivity of Ni-doped La1.99Sr0.01CuO4 single crystals grown by Traveling-Solvent Floating-Zone technique. Our data shows that in lightly Sr-doped compounds the Neel temperature T-N increased with increasing Ni concentration. At high temperatures, the resistivity is described within the impurity band conduction model. As the temperature is lowered, the resistivity behavior change to the variable range hopping model associated with the evolving of antiferromagnetic ordering. - S Lee; A Yamamoto; H Mori; Y Eltsev; T Masui; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 378 (Part 1) 33 - 37 0921-4534 2002/10 [Refereed]
Here, we report the growth of magnesium diboride (MgB2) single crystals under high-pressure in the Mg-B-N system. The phase stability limit of MgB2 in P-T space was determined and reaction diagram for the crystal growth of MgB2 under high-pressure was proposed. It was found that utilization of longitudinal temperature gradient and optimisation of reactant pellets locations in the BN high-pressure cell is very helpful for reproducible growth of MgB2 single crystals of various shapes and size of 200-700 mum. The high-quality of the samples was confirmed by single crystal X-ray diffraction and sharp superconducting transitions at T-c = 38.1-38.3 K obtained in both magnetization (DeltaT(c) = 0.6 K) and resistivity (DeltaT(c) = 0.3 K) measurements. (C) 2002 Elsevier Science B.V. All rights reserved. - T Masui; S Lee; A Yamamoto; S TajimaPHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS ELSEVIER SCIENCE BV 378 (Part 1) 216 - 219 0921-4534 2002/10 [Refereed]
We report the ab-plane and c-axis resistivity of MgB2 single crystals. The absolute value of the c-axis resistivity is one to two orders of magnitude larger than the in-plane resistivity. The temperature dependencies are almost the same in both directions. Anisotropy in the superconducting state is determined from the resistivity measurements under magnetic field. This is compared to the anisotropy estimated from the normal state resistivity. The fairly good agreement of anisotropy ratio in the normal and superconducting state implies that electronic state of MgB2 can be analyzed within the three-dimensional effective mass model. (C) 2002 Elsevier Science B.V. All rights reserved. - S Tajima; T Masui; H Uchiyama; JW Quilty; Y Eltsev; S Lee; A Yamamoto; H MoriCURRENT APPLIED PHYSICS ELSEVIER SCIENCE BV 2 (4) 315 - 319 1567-1739 2002/08 [Refereed]
Thanks to the high quality single crystals of MgB2, we have measured various physical properties to extract important features of the electronic state in this superconductor. The electron density maps calculated from a precise X-ray diffraction analysis and the band dispersions determined by the angle-resolved photoemission spectroscopy demonstrate that the boron orbitals play a central role, just as predicted by the band theory. The strong coupling of the high frequency optical phonon with the boron bands is indicated in resistivity and Raman scattering spectra. Although the multi-band structure significantly affects various normal state properties, no clear multi-gap feature can be observed in the Raman scattering spectra below T-c. (C) 2002 Elsevier Science B.V. All rights reserved. - T Masui; K Yoshida; S Lee; A Yamamoto; S TajimaPHYSICAL REVIEW B AMERICAN PHYSICAL SOC 65 (21) 214513-1 - 214513-4 1098-0121 2002/06 [Refereed]
We extract phonon contributions from the transport properties of a MgB2 single crystal. The temperature dependence of the in-plane resistivity is well explained by the Bloch-Gruneisen formula with the Debye temperature Theta(D)similar to400 K, taking into account an additional contribution of the E-2g phonon mode (similar to890 K). In the thermoelectric power, we find a phonon drag peak around 70 K, which gives a consistent estimation of Theta(D) with the resistivity result. The pressure dependence of the in-plane resistivity reveals a major contribution of the E-2g phonon mode to superconductivity. - A Tonomura; H Kasai; O Kamimura; T Matsuda; K Harada; T Yoshida; T Akashi; J Shimoyama; K Kishio; T Hanaguri; K Kitazawa; T Masui; S Tajima; N Koshizuka; PL Gammel; D Bishop; M Sasase; S OkayasuPHYSICAL REVIEW LETTERS AMERICAN PHYSICAL SOC 88 (23) 237001-1 - 237001-4 0031-9007 2002/06 [Refereed]
In order to elucidate the formation mechanism of unconventional arrangements of vortices in high-T-c superconducting thin films at an inclined magnetic field to the layer plane, we investigated the structures of vortex lines inside the films by Lorentz microscopy using our 1-MV field-emission electron microscope. Our observation results concluded that vortex lines are tilted to form linear chains in YBaCu3 O-7,O-8 . Vortex lines in the chain-lattice state in Bi2Sr 2CaCu2O (8+delta) , on the other hand, are all perpendicular to the layer plane, and therefore only vortices lined up along Josephson vortices form chains. - S Lee; H Mori; T Masui; Y Eltsev; A Yamamoto; S TajimaJOURNAL OF THE PHYSICAL SOCIETY OF JAPAN PHYSICAL SOC JAPAN 70 (8) 2255 - 2258 0031-9015 2001/08 [Refereed]
Here we report the growth of sub-millimeter MgB2 single crystals of various shapes under high pressure in Mg-B-N system. Structure refinement using a single-crystal X-ray diffraction analysis gives lattice parameters a = 3.0851(5) Angstrom and c = 3.5201(5) Angstrom with small reliability factors R-w = 0.025, R = 0.018), which enables us to analyze the Fourier and Fourier difference maps. The maps clearly show the B sp(2) orbitals and covalency of the B-B bonds. The sharp superconducting transitions at T-c = 38.1-38.3 K were obtained in both magnetization DeltaT(c) = 0.6 K) and resistivity (DeltaT(c) < 0.3 K) measurements. Resistivity measurements with magnetic fields applied parallel and perpendicular to the NI-g and B sheets reveal the anisotropic nature of this compound, with upper critical field anisotropy ratio of about 2.7. - T Masui; T IshiguroSYNTHETIC METALS ELSEVIER SCIENCE SA 117 (1-3) 15 - 19 0379-6779 2001/02 [Refereed]
In ClO4--doped v-polyacetylene with the dopant concentration of 2-6%, the ESR susceptibility was found to decrease below 200 K. Meanwhile, the thermoelectric power did not exhibit the corresponding anomaly, although the resistivity showed a change suggesting a variation in the carrier dynamics. The ESR line-shape analysis revealed that a phase separation due to droplet nucleation undergoes in a mixed phase of a soliton state associated with spin-charge separation and a polaron state. For the 2.6% doped, the spin-charge separated state appeared with negligible content of the metallic phase, suggesting that the upper bound for a homogeneous soliton state is similar to3% in the dopant concentration. The superconductivity by frustration mechanism is considered to be pre-empted by the soliton phase. (C) 2001 Elsevier Science B.V. All rights reserved. - T. Masui; S. TajimaPhysica C: Superconductivity and its Applications 357-360 (Part 1) 39 - 41 0921-4534 2001 [Refereed]
Effects of impurity substitution on vortex dynamics have been investigated in various underdoped YBa2Cu3O7-y. Measuring the irreversibility line, the M-H curve and the T-dependence of magnetization in the reversible region, we compared the results of the pure and the Zn-substituted crystals with the same Tc. It was found that the magnetic properties below Tc are almost identical between them, in spite of different doping and impurity levels. This indicates that Tc rather than anisotropy ratio or amount of disorder is a primary factor for determining vortex behaviors in the underdoped regime. © 2001 Elsevier Science B.V. - T Masui; K Tomimoto; S TajimaADVANCES IN SUPERCONDUCTIVITY XII SPRINGER-VERLAG TOKYO 12 221 - 223 2000 [Refereed]
We measured out-of-plane resistivity (rho(c)) for pure and Zn/Ni substituted YBa2Cu3O7-delta single crystals in the underdoped regime where the incoherent carrier transport is observed. In the heavily underdoped regime, Zn/Ni substitution to the Cu sites suppresses the increase of rho(c) at low temperatures, resulting in the reduction of anisotropy in the normal state. For highly doped crystals, we also report Zn substitution effect on the anisotropy of coherence length as a function of oxygen content. - T Masui; T Ishiguro; J TsukamotoSYNTHETIC METALS ELSEVIER SCIENCE SA 104 (3) 179 - 188 0379-6779 1999/07 [Refereed]
We present the results of ESR, thermoelectric power, and resistivity measurements for perchlorate doped polyacetylene. An anomaly similar to a spin-gap was observed in the spin susceptibility in the intermediate dopant-concentration region. Since a corresponding anomaly was not observed in the thermoelectric power, the comparison leads us to conclude that the anomaly is associated with spin-charge separation, in relation to the formation of charged soliton-like carrier, as a result of phase separation. The resistivity data show a decreasing tendency in the activation energy on the low-temperature side of the transition, suggesting a change in carrier transport. The absence of similar data in previous reports is discussed in terms of structural difference in polyacetylene chains. The low-temperature heat capacity measurement carried out as a function of the dopant-concentration revealed that the chain arrangement to form channels to accommodate the dopants is almost formed at the initiation of doping. (C) 1999 Elsevier Science S.A. All rights reserved. - T Masui; T Ishiguro; J TsukamotoSYNTHETIC METALS ELSEVIER SCIENCE SA 101 (1-3) 347 - 348 0379-6779 1999/05 [Refereed]
A notable decrease in ESR spin susceptibility was found near 130 K in intermediately ClO4--doped upsilon-(CH)(x). The absence of the corresponding change in thermoelectric power suggests that it is associated with a spin-charge separation. The possible origin is discussed with respect to the structural change in (CH)(x). - T Masui; T Ishiguro; J TsukamotoPHYSICAL REVIEW LETTERS AMERICAN PHYSICAL SOC 82 (10) 2151 - 2154 0031-9007 1999/03 [Refereed]
Transition to a spin-gap state in a doped conducting polymer is reported for the first time. A decrease in the ESR spin susceptibility was observed near 200 K in trans-polyacetylene doped with perchloric ion (ClO4-). The thermoelectric power did not show any corresponding anomaly, while the activation energy of the resistivity was decreased slightly on the spin-gap formation. These results suggest that the electronic state undergoes a spin-charge separation and the carriers are actuated by lower energy. It was also shown, by the lattice heat capacity measurement, that the lattice structure, connected to the framework for the soliton lattice, is changed remarkably at the initial stage of doping. - T Masui; T Ishiguro; J TsukamotoPHYSICAL REVIEW B AMER PHYSICAL SOC 58 (8) 4352 - 4361 1098-0121 1998/08 [Refereed]
The low-temperature metallic conductance in FeCl4-- and ClO4--doped polyacetylene has been studied with the aim to probe the conduction electron-dopant interaction. A different behavior ascribable to the magnetic moment at the dopant site was found below similar to 1 K under a magnetic field of less than similar to 1 T. The result is discussed with respect to the effect of scattering by localized spins at the FeCl4- site. The logarithmic temperature dependence and the negative magnetoresistance are examined in relation to spin scattering at the magnetic dopant and at the carbonyl basis, and to pseudospin scattering due to dynamic chain distortion. The effect of inhomogeneity is discussed also. - T Masui; T Ishiguro; J Tsukamoto; A TakahashiSYNTHETIC METALS ELSEVIER SCIENCE SA LAUSANNE 84 (1-3) 867 - 868 0379-6779 1997/01 [Refereed]
Motivated by the conjecture of superconductivity by Kivelson and Emery (Synth. Met. 65 (1994) 249), we have carried out the low-field ESR measurements for intermediately either FeCl4- or ClO4- doped polyacetylenes. A trace of superconductivity was absent, and as reasons effects of doping phase separation and of disorder are remarked. - TH Gilani; T Masui; GY Logvenov; T IshiguroSYNTHETIC METALS ELSEVIER SCIENCE SA LAUSANNE 78 (3) 327 - 331 0379-6779 1996/04 [Refereed]
The Hall coefficient and the thermoelectric power of PF6-doped polypyrrole exhibiting metallic temperature dependence in the resistivity below 20 K are presented. It is remarkable that the Hall coefficient is negative and increases by cooling down to 0.5 K, in contrast to the acceptor doping and the decrease in the resistivity. The thermoelectric power becomes almost zero or weakly negative in the metallic region although it is positive and has almost linear temperature dependence above 50 K. It is also shown that the onset temperature of the metallic conductance is raised by the pressure.
Works
MISC
- Tanaka K.; Hieu N.T.; Masui T.; Miyasaka S.; Tajima S.; Sasagawa T. Meeting abstracts of the Physical Society of Japan 69- (1) 567 -567 2014/03
- UYKUR E.; TANAKA K.; MASUI T.; MIYASAKA S.; TAJIMA S. Meeting abstracts of the Physical Society of Japan 68- (2) 500 -500 2013/08
- Hieu N.T.; Tanaka K.; Masui T.; Miyasaka S.; Tajima S.; Sasagawa T. Meeting abstracts of the Physical Society of Japan 68- (2) 500 -500 2013/08
- UYKUR E.; TANAKA K.; MASUI T.; MIYASAKA S.; TAJIMA S. Meeting abstracts of the Physical Society of Japan 68- (1) 656 -656 2013/03
- Kamiya Keisuke; Masui Takahiko; Bando Hiroshi; Aiura Yoshihiro; Tajima Setsuko Meeting abstracts of the Physical Society of Japan 68- (1) 600 -600 2013/03
- Kamiya Keisuke; Masui Takahiko; Tajima Setsuko Meeting abstracts of the Physical Society of Japan 67- (2) 566 -566 2012/08
- UYKUR E.; TANAKA K.; MASUI T.; MIYASAKA S.; TAJIMA S. Meeting abstracts of the Physical Society of Japan 67- (2) 583 -583 2012/08
- Murai N.; Masui T.; Tajima S.; Ishikado M.; Ishida S.; Eisaki H.; Uchida S. Meeting abstracts of the Physical Society of Japan 67- (2) 583 -583 2012/08
- Murai N.; Masui T.; tajima S.; Ishikado M.; Ishida S.; Eisaki H.; Uchida S. Meeting abstracts of the Physical Society of Japan 66- (2) 659 -659 2011/08
- Iwasawa H.; Yoshida Y.; Hase I.; Eisaki H.; Masui T.; Tajima S.; Shimada K.; Namatame H.; Taniguchi M.; Dessau D. S.; Aiura Y. Meeting abstracts of the Physical Society of Japan 66- (2) 660 -660 2011/08
- Tadatomo H.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 65- (1) 549 -549 2010/03
- Hirata W.; Masui T.; Miyasaka S.; Tajima S.; Ishikado M.; Iyo A.; Kihou K.; Kito H.; Eisaki H.; Shamoto S. Meeting abstracts of the Physical Society of Japan 64- (2) 470 -470 2009/08
- Tadatomo H.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 64- (2) 480 -480 2009/08
- Mikasa Y.; Masui T.; Lee Sergey; Tajima S. Meeting abstracts of the Physical Society of Japan 64- (1) 655 -655 2009/03
- Iwasawa H.; Douglas J. F.; Sato K.; Masui T.; Yoshida E. Y.; Sun Z.; Eisaki H.; Bando H.; Ino A.; Arita M.; Shimada K.; Namatame H.; Taniguchi M.; Tajima S.; Uchida S.; Saitoh T.; Dessau D. S.; Aiura Y. Meeting abstracts of the Physical Society of Japan 63- (2) 559 -559 2008/08
- Sato K.; Aiura Y.; Nishihara Y.; Yoshida Y.; Eisaki H.; Bando H.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 63- (2) 559 -559 2008/08
- Okawa M.; Ishizaka K.; Kiss T.; Shimojima T.; Togashi T.; Watanabe S.; Wang X.-Y; Chen C.-T.; Uchiyama H.; Masui T.; Tajima S.; Saitoh T.; Shin S. Meeting abstracts of the Physical Society of Japan 63- (2) 558 -558 2008/08
- Mikasa Y.; Suemitsu N.; Masui T.; Lee Sergey; Tajima S. Meeting abstracts of the Physical Society of Japan 63- (2) 522 -522 2008/08
- Suzuki S.; Saijo S.; Mikasa Y.; Masui T.; Miyasaka S.; Tajima S. Meeting abstracts of the Physical Society of Japan 63- (2) 446 -446 2008/08
- Sato K.; Iwasawa H.; Douglas J.F.; Aiura Y.; Nishihara Y.; Saitoh T.; Yoshida Y.; Eisaki H.; Bando H.; Ino A.; Arita M.; Shimada K.; Namatame H.; Taniguchi M.; Masui T.; Tajima S.; Uchida S.; Dessau D.S. Meeting abstracts of the Physical Society of Japan 63- (1) 607 -607 2008/02
- Nagasao Kouta; Masui Takahiko; Tajima Setsuko Meeting abstracts of the Physical Society of Japan 63- (1) 628 -628 2008/02
- Nishikawa K.; Masui T.; Tajima S.; Eisaki H.; Kito H.; Iyo A. Meeting abstracts of the Physical Society of Japan 63- (1) 631 -631 2008/02
- Uraike Yuta; Masui Takahiko; Tajima Setsuko Meeting abstracts of the Physical Society of Japan 63- (1) 576 -576 2008/02
- Okawa M.; Ishizaka K.; Kiss T.; Shimojima T.; Togashi T.; Watanabe S.; Wang X. Y.; Chen C. T.; Uchiyama H.; Masui T.; Tajima S.; Saitoh T.; Shin S. Meeting abstracts of the Physical Society of Japan 62- (2) 554 -554 2007/08
- Iwasawa H.; Aiura Y.; Saitoh T.; Yoshida Y.; Eisaki H.; Bando H.; Iwase T.; Ino A.; Arita M.; Shimada K.; Namatame H.; Taniguchi M.; Masui T.; Tajima S.; Uchida S.; Dessau D.S. Meeting abstracts of the Physical Society of Japan 62- (1) 492 -492 2007/02
- Masui T.; Hiramachi T.; Tajima S. Meeting abstracts of the Physical Society of Japan 62- (1) 509 -509 2007/02
- Fujita K.; Lee J.; Wang M.; McElroy K.; Slezak A.; Aiura Y.; Bando H.; Ishikado M.; Masui T.; Zhu J.-X.; Balatsky A. V.; Eisaki H.; Uchida S.; Davis J .C. Meeting abstracts of the Physical Society of Japan 62- (1) 507 -507 2007/02
- Chabayashi K.; Masui T.; Miyasaka S.; Tajima S.; Fujioka J.; Tokura Y. Meeting abstracts of the Physical Society of Japan 62- (1) 510 -510 2007/02
- Nishikawa K.; Masui T.; Tajima S.; Eisaki H.; Kito H.; Iyo A. Meeting abstracts of the Physical Society of Japan 62- (1) 509 -509 2007/02
- Nagasao Kota; Masui Takahiko; Tajima Setsiiko Meeting abstracts of the Physical Society of Japan 62- (1) 596 -596 2007/02
- Uraike Yuta; Masui Takahiko; Tajima Setsuko Meeting abstracts of the Physical Society of Japan 62- (1) 596 -596 2007/02
- Hiramachi T.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 61- (2) 461 -461 2006/08
- Masui T.; Fujita K.; Eisaki H.; Tajima S.; Uchida S. Meeting abstracts of the Physical Society of Japan 61- (2) 438 -438 2006/08
- Chabayashi K.; Masui T.; Miyasaka S.; Tajima S.; Fujioka J.; Tokura Y. Meeting abstracts of the Physical Society of Japan 61- (2) 442 -442 2006/08
- Okawa M.; Ishizaka K.; Kiss T.; Shimojima T.; Saitoh T.; Togashi T.; Watanabe S.; Zhang C.Q.; Chen C.T.; Uchiyama H.; Masui T.; Tajima S.; Shin S. Meeting abstracts of the Physical Society of Japan 61- (2) 519 -519 2006/08
- Iwasawa H.; Aiura Y.; Saitoh T.; Eisaki H.; Bando H.; Yamasaki T.; Kamo T.; Anzai H.; Ino A.; Arita M.; Masui T.; Tajima S.; Uchida S.; Ishikado M.; Fujita K.; Dcssau D.S.; Douglas J.F.; Sun Z. Meeting abstracts of the Physical Society of Japan 61- (1) 641 -641 2006/03
- Suemitsu N.; Masui T.; Lee Sergey; Tajima S. Meeting abstracts of the Physical Society of Japan 61- (1) 509 -509 2006/03
- Kakeshita T.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 61- (1) 624 -624 2006/03
- Fukuda Tatsuo; Baron Alfred Q. R.; Sutter John P.; Mizuki Jun'ichiro; Hoesch Moritz; Tsutsui Satoshi; Tajima Setsuko; Masui Takahiko; Uchiyama Yuji; Endoh Yasuo Meeting abstracts of the Physical Society of Japan 60- (2) 432 -432 2005/08
- Suemitsu N.; Masui T.; Lee Sergey; Tajima S. Meeting abstracts of the Physical Society of Japan 60- (2) 494 -494 2005/08
- Kakeshita T.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 60- (2) 388 -388 2005/08
- Masui T.; Hiramachi T.; Ohmichi E.; Kajita K.; Osada T.; Tajima S. Meeting abstracts of the Physical Society of Japan 60- (1) 605 -605 2005/03
- Ishii K; Tajima S; Murakami Y; Mizuki J; Tsutsui K; Endoh Y; Tbhyama T; Kuzushita K; Inami T; Ohwada K; Maekawa S; Masui T Meeting Abstracts of the Physical Society of Japan 60- (0) 514 -514 2005
- Ishii K; Maekawa S; Masui T; Tajima S; Yamada K; Tsutsui K; Endoh Y; Tohyama T; Hoesch Moritz; Tsubota M; Inami T; Mizuki J; Murakami Y Meeting Abstracts of the Physical Society of Japan 60- (0) 356 -356 2005
- Kakeshita T.; Masui T; Tajima S Meeting abstracts of the Physical Society of Japan 59- (2) 442 -442 2004/08
- Masui T.; Limonov M.; Uchiyama H.; Tajima S.; Yamanaka A. Meeting abstracts of the Physical Society of Japan 59- (2) 441 -441 2004/08
- Fukuda Tatsuo; Mizuki Junichiro; Endoh Yasuo; Alfred Q. R. Baron; John P. Sutter; Tsutsui Satoshi; Tajima Setsuko; Uchiyama Yuji; Masui Takahiko Meeting abstracts of the Physical Society of Japan 59- (2) 461 -461 2004/08
- Uchiyama H; Masui T; Tajima S Meeting abstracts of the Physical Society of Japan 59- (1) 594 -594 2004/03
- Kakeshita T.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 59- (1) 520 -520 2004/03
- Masui T; Lee S; Tajima S Meeting abstracts of the Physical Society of Japan 59- (1) 649 -649 2004/03
- Ohmichi E; Lee S; Masui T; Tajima S; Osada T Meeting abstracts of the Physical Society of Japan 59- (1) 649 -649 2004/03
- Ohmichi E.; Lee S.; Masui T.; Tajima S.; Osada T. Meeting abstracts of the Physical Society of Japan 58- (2) 558 -558 2003/08
- Masui T.; Lee S.; Uchiyama H.; Yamamoto A.; Tajima S. Meeting abstracts of the Physical Society of Japan 58- (2) 559 -559 2003/08
- Masui T.; Limonov M.; Uchiyama H.; Tajima S.; Yamanaka A. Meeting abstracts of the Physical Society of Japan 58- (1) 543 -543 2003/03
- Takano Y.; Masui T.; Yoshida K.; Tajima S. Meeting abstracts of the Physical Society of Japan 58- (1) 598 -598 2003/03
- Lee S.; Masui T.; Yamamoto A.; Uchiyama H.; Tajima S. Meeting abstracts of the Physical Society of Japan 58- (1) 490 -490 2003/03
- Masui T; Lee S; Tajima S Meeting abstracts of the Physical Society of Japan 57- (2) 525 -525 2002/08
- Yamamoto A; Takao T; Masui T; Izumi M; Tajima S Meeting abstracts of the Physical Society of Japan 57- (2) 526 -526 2002/08
- Limonov M; Masui T; Lee S; Uchiyama H; Tajima S; Yamanaka A Meeting abstracts of the Physical Society of Japan 57- (2) 472 -472 2002/08
- Masui T.; Lee S.; Yamamoto A.; Tajima S. Meeting abstracts of the Physical Society of Japan 57- (1) 502 -502 2002/03
- Uchiyama H.; Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 57- (1) 558 -558 2002/03
- Sergey Lee; 山本文子; 森初果; 増井孝彦; 内山裕士; James Quilty; 田島節子 固体物理 37- (3) 51 -57 2002
- Yoshida K.; Masui T.; Lee S.; Yamamoto A.; Tajima S. Meeting abstracts of the Physical Society of Japan 56- (2) 502 -502 2001/09
- Yamamoto A.; Takao C.; Masui T.; Izumi M.; Tajima S. Meeting abstracts of the Physical Society of Japan 56- (2) 500 -500 2001/09
- Masui T.; Tajima S. Meeting abstracts of the Physical Society of Japan 56- (1) 557 -557 2001/03
- Masui T.; Yoshida K.; Tajima S. Meeting abstracts of the Physical Society of Japan 55- (1) 454 -454 2000/03
- Yoshida K; Masui T; Tajima S Meeting abstracts of the Physical Society of Japan 54- (2) 518 -518 1999/09
- MASUI T.; ISHIGURO T.; TSUKAMOTO J. Meeting abstracts of the Physical Society of Japan 53- (1) 264 -264 1998/03
- Masui T.; Ishiguro T.; Tsukamoto J. Meeting abstracts of the Physical Society of Japan 52- (2) 267 -267 1997/09
- 増井孝彦 物性研究 67- (4) 448 -467 1997/01
- Masui T.; Ishiguro T.; Tukamoto J.; Tanaka A. Abstracts of the meeting of the Physical Society of Japan. Annual meeting 51- (2) 391 -391 1996/03
- Masui T; T.H Gilani; Ishiguro T Abstracts of the meeting of the Physical Society of Japan. Sectional meeting 1995- (2) 339 -339 1995/09
- 山内康寛; 増井孝彦; 山田耕作 物性研究 64- (2) 111 -115 1995/05
Research Grants & Projects
- Japan Society for the Promotion of Science：Grants-in-Aid for Scientific ResearchDate (from‐to) : 2012/04 -2015/03Author : TAJIMA Setsuko; MIYASAKA Shigeki; MASUI Takahiko; TANAKA Kiyohisa; TOHYAMA Takami; UYKUR EceWe studied the pseudogap problem of the cuprates that is most important to elucidate the high temperature superconductivity mechanism. It has been clarified from the measurements of optical spectra that the pseudogap coexists with superconducting gap and not a precursor of superconductivity. A precursor of superconductivity was independently observed between the peusdogap temperature and superconducting temperature Tc. It was also revealed that the precursor temperature decreases with doping, being different from that of Tc, which suggests the importance of electron correlation for Cooper pairing. It is likely that the coexistence of pseudogap and superconducting gap causes the anomalous properties of superconducting gap.
- Japan Society for the Promotion of Science：Grants-in-Aid for Scientific ResearchDate (from‐to) : 2007 -2010Author : AIURA Yoshihiro; EISAKI Hiroshi; MASUI Takahiko; YOSHIDA Yoshiyuki; IWASAWA HideakiAngle-resolved photoemission spectroscopy with low-energy tunable photons along the nodal direction of oxygen isotope substituted Bi_2Sr_2CaCu_2O_<8+δ> reveals a distinct oxygen isotope shift near the electron-boson coupling "kink" in the electronic dispersion. The magnitude (a few meV) and direction of the kink shift are as expected due to the measured isotopic shift of phonon frequency, and are also in agreement with theoretical expectations. This demonstrates the participation of the phonons as dominant players, as well as pinpointing the most relevant of the phonon branches.
- Japan Society for the Promotion of Science：Grants-in-Aid for Scientific ResearchDate (from‐to) : 2007 -2010Author : TAJIMA Setsuko; MIYASAKA Shigeki; MASUI Takahiko; TANAKA Kiyohisa; ALFRED Baron; TADATOMO Hirki; ECE Uykur; SAKAI Yusuke; MIKASA Yuji; HOSSEIN Khosroabadi; KOBAYASHI Jun-ichi; MATSUOKA Teppei; FUJIMOTO Takashi; NAGASAO Kota; URAIKE Yuta; NISHIKAWA Kazutaka; HIRAMACHI TakayukiWe have investigated the electronic state of various high-Tc cuprates such as (Y, Ca)Ba_2Cu_3O_y, by using Raman scattering, optical reflectivity and transport measurements. We found that the polarization dependence of Raman scattering that is typical for d-wave superconductors is lost when a pseudogap is closed, and that carrier overdoping induces unpaired carriers due to some mechanism different from a usual impurity pair-breaking. All these results strongly suggest that the electronic state in the overdoped regime is intrinsically inhomogeneous.
- 日本学術振興会：科学研究費助成事業Date (from‐to) : 2007 -2008Author : 宮坂 茂樹; 田島 節子; 増井 孝彦本研究では、"低次元遷移金属化合物"、"量子臨界点近傍の新規異常物性"をキーワードとして、1次元、2次元遷移金属酸化物と化合物を対象に、化学的な見地から新規物質探索や元素置換効果による電子相制御を行い、量子臨界点近傍の新奇な現象を開拓することを目的としていた。初年度に引き続き2次元オキシニクタイト鉄系超伝導体の研究を継続して行ってきた。LaFePO_<1-x>F_xの多結晶資料を用いた輸送現象、比熱などの研究の結果、以下のことが明らかとなった。電気抵抗率の低温の温度依存性は、温度の2乗に比例しており、本系でも電子相関の効果が物性に影響を与えていることが判明したが、一方で常伝導状態下での電子比熱係数は約10mJ/molK^2とそれほど大きな値は示さず、その効果はモット転移系などと比較すると比較的小さいものであることが判明した。室温付近のホール係数はほとんど温度に依存せず、その値からはFe-サイトあたり、電子が0.1個供給されていることを意味し、本系は少数キャリア系であることを示唆している。また、磁場中での電気抵抗率の測定からは、2次元超伝導体特有の超伝導転移のブロードニングが観測され、また臨界磁場Hc2の温度依存性からは、本系がマルチバンド系であることを示唆する結果が得られている。本系の類似系であるLaFeAsO_<1-x>F_xの多結晶試料や(BaK)Fe_2As_2単結晶に関しても、育成に成功しており、今後の研究を通して、P系、As系の超伝導転移温度や超伝導発現メカニズムの違いに関する研究を継続して行う。
- Japan Society for the Promotion of Science：Grants-in-Aid for Scientific ResearchDate (from‐to) : 2005 -2006Author : TAJIMA Setsuko; FUJII Kenichi; MASUI TakahikoSingle crystals of (Y, Ca)Ba_2Cu_3O_y were grown by a pulling technique and then detwinned by annealing in oxygen atmosphere under uniaxial pressure, followed by post-annealing in O_2 for controlling carrier concentration. In this way, we have obtained samples large enough for Terahertz spectroscopy (〜3x3 mm^2). As to the method for reflectivity measurement in the low frequency region, we have changed from the original plan of usual method with use of BWO tube as a light source to the new method of time domain spectroscopy (TDS) with use of Ti-Sapphire ultra-fast pulse laser. The TDS method is usually carried out with a geometry of transmittance measurement, while there are many difficulties in measurement with a reflectance geometry. The low temperature measurement for samples within a cryostat also gives some additional difficulties. In order to overcome these difficulties, we have improved an optical system as well as a sample holder. The test measurement for a gold mirror and (La,Sr)_2CuO_4 superconductor gave us a satisfactory result. We also measured far-infrared reflectivity spectra of detwinned (Y, Ca)Ba_2Cu_3O_y with polarization parallel to a-and/or b-axes. The a-axis spectrum is expected to represent the charge response within the CuO_2-plane. Compared to the a-axis spectrum for optimally doped YBa_2Cu_3O_y, the spectrum for carrier overdoped sample was found to show lower reflectivity (<100%) even at T≪T_c, which suggests a presence of unpaired carriers. It was also found that this low reflectivity tendency becomes more pronounced in the further overdoped (Y, Ca)Ba_2Cu_3O_y. A possible origin for the unpaired carriers is that some pair-breaking is driven by carrier overdoping or that the phase separation of superconducting and non-superconducting regions takes place. This is very important findings to understand the electronic phase diagram of high-T_c superconductors.
- 日本学術振興会：科学研究費助成事業Date (from‐to) : 2005 -2006Author : 田島 節子; 増井 孝彦昨年度に引き続き、Ca置換したYBa_2Cu_3O_yの結晶を育成し、酸素濃度とCa濃度の制御によってキャリア濃度を様々に変化させた。これらの試料を用いて、ラマン散乱スペクトルと光学反射スペクトルの測定を行った。 ラマン散乱分光からは、キャリア過剰ドーピングの効果として、二つの異常な振る舞いが観測された。1つは、B_<1g>偏光における超伝導対破壊ピークのエネルギーが激減し、ピーク強度が増大すること。もう一つは、yy偏光での対破壊ピークの強度が著しく減少すること、である。このようなスペクトルの変化は、キャリア濃度にのみ依存しており、酸素欠損量との相関はないことが明らかになった。前者のスペクトル異常の原因としては、超伝導ギャップの対称性が純粋なd波からs波成分の混じったものに変化していることが考えられる。後者のスペクトル異常は、面間の結合が強まったため、CuO鎖とCuO_2面の電子ラマン成分が負の干渉を起こした結果であると解釈される。 興味深いことは、これらのスペクトル異常のキャリア濃度依存性が、キャリア濃度p=0.18-0.19付近で急激に変化することである。前者の異常は、p=0.19に向かって急激な変化をし、それ以上のキャリア濃度では変化が極めて小さい。一方、後者の異常は、p=0.19以上から現れはじめる。このことは、p=0.19付近で何らかの電子状態の大きな変化が起きていることを示唆するものと考えられる。 面内光学反射率スペクトルからは、キャリアを過剰ドープするに従って、超伝導対形成をしない残留キャリア成分が増加し、同時に超流動密度(超伝導キャリア数)が減少する様子が観測された。これは、キャリアを過剰にドープすることが、なんらかの対破壊効果を引き起こしているか、或は、超伝導組成と非超伝導金属組成とに分離しているような不均一電子状態になっているか、どちらかではないかと思われる。
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