研究者詳細 - 横谷　尚睦

論文 - 横谷　尚睦

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Yokoya et al. Reply

T. Yokoya, A. Chainani, T. Takahashi, T. Katayama-Yoshida, M. Kasai, Y. Tokura

Physical Review Letters 78 ( 11 ) 2272 1997年

High-resolution angle-resolved photoemission study of CeP: Narrow-band formation of 4f electrons

H. Kumigashira, S. Yang, T. Yokoya, A. Chainani, T. Takahashi, A. Uesawa, T. Suzuki

Physical Review B - Condensed Matter and Materials Physics 55 ( 6 ) R3355 - R3357 1997年

記述言語：英語掲載種別：研究論文（学術雑誌）

High-resolution angle-resolved photoemission spectroscopy at low temperature has been performed on the low-carrier Kondo material CeP. It was found that the p-f bonding state with a dominant 4f character exhibits a finite-energy dispersion of about 40 meV along the ΓX direction in the Brillouin zone. This implies that 4f electrons in CeP form a narrow band owing to the strong anisotropic p-f and d-f mixing. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.55.R3355

Paramagnetic-to-antiferroparamagnetic phase transition of CeSb studied by high-resolution angle-resolved photoemission

H. Kumigashira, H. Kim, A. Ashihara, A. Chainani, T. Yokoya, T. Takahashi, A. Uesawa, T. Suzuki

Physical Review B - Condensed Matter and Materials Physics 56 ( 21 ) 13654 - 13657 1997年

記述言語：英語掲載種別：研究論文（学術雑誌）

The paramagnetic-to-antiferroparamagnetic phase transition of CeSb has been studied by high-resolution angle-resolved photoemission spectroscopy. The hole and electron pockets are clearly observed at the Brillouin-zone center and boundary, respectively. The volume of both hole and electron pockets increases when the temperature is lowered across the magnetic phase transition (Formula presented). The observed change of Fermi-surface topology is discussed in terms of the temperature-dependent anisotropic (Formula presented) mixing. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.56.13654

Angle-resolved photoemission spectroscopy study of the superconducting gap anisotropy in Bi2Sr2CaCu2O8+x 査読

H Ding, MR Norman, JC Campuzano, M Randeria, AF Bellman, T Yokoya, T Takahashi, T Mochiku, K Kadowaki

PHYSICAL REVIEW B 54 ( 14 ) R9678 - R9681 1996年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report measurements of the momentum dependence of die superconducting gap in Bi2Sr2CaCu2O8+x with angle-resolved photoemission spectroscopy using a dense sampling of the Brillouin zone in the vicinity of the Fermi surface. In the Y quadrant of the zone, where there are no complications from ghost bands caused by the superlattice, we find a gap function consistent within error bats to the form cos(k(x))-cos(k(y)) expected for a d-wave order parameter. Similar results are found in the X quadrant with the photon polarization chosen to enhance main band emission over that due to ghost bands.

Angle-resolved photoemission spectroscopy study of the superconducting gap anisotropy in Bi2Sr2CaCu2O8+x

Ding H., Norman M. R., Campuzano J. C., Randeria M., Bellman A. F., Yokoya T., Takahashi T., Mochiku T., Kadowaki K.

Physical review B 54 ( 14 ) R9678-R9681 - R9681 1996年10月

記述言語：英語出版者・発行元：American Physical Society

We report measurements of the momentum dependence of the superconducting gap in Bi2Sr2CaCu2O8+x with angle-resolved photoemission spectroscopy using a dense sampling of the Brillouin zone in the vicinity of the Fermi surface. In the Y quadrant of the zone, where there are no complications from ghost bands caused by the superlattice, we find a gap function consistent within error bars to the form cos(kx)-cos(ky) expected for a d-wave order parameter. Similar results are found in the X quadrant with the photon polarization chosen to enhance main band emission over that due to ghost bands.

DOI： 10.1103/PhysRevB.54.R9678

High-resolution angle-resolved photoemission spectroscopy of the momentum dependence of the superconducting gap in Bi2Sr2CaCu2O8

Yokoya T., Takahashi T., Mochiku T., Kadowaki K.

Physical review B 53 ( 21 ) 14055 - 14057 1996年6月

記述言語：英語出版者・発行元：American Physical Society

The momentum dependence of the superconducting gap in Bi2Sr2CaCu2O8 has been studied using high-resolution angle-resolved photoemission spectroscopy with nonpolarized light. The size of the superconducting gap obtained at several points on the Fermi surface shows a linear dependence with respect to the gap function of the dx2-y2 wave defined as 0.5coskxa-coskya. This suggests that the anomaly in the superconducting gap observed with polarized synchrotron-radiation light is not intrinsic, being probably due to the superstructure of the BiO plane, and rather the strong anisotropy of the superconducting gap, like the dx2-y2 symmetry, is intrinsic.

DOI： 10.1103/PhysRevB.53.14055

Direct observation of particle-hole mixing in the superconducting state by angle-resolved photoemission

Campuzano J. C., Ding H., Norman M. R., Randeira M., Bellman A. F., Yokoya T., Takahashi T., Katayama-Yoshida H., Mochiku T., Kadowaki K.

Physical review B 53 ( 22 ) R14737-R14740 - R14740 1996年6月

記述言語：英語出版者・発行元：American Physical Society

Particle-hole (p-h) mixing is a fundamental consequence of the existence of a pair condensate. We present direct experimental evidence for p-h mixing in the angle-resolved photoemission (ARPES) spectra in the superconducting state of Bi2Sr2CaCu2O8+δ. In addition to its pedagogical importance, this establishes unambiguously that the gap observed in ARPES is associated with superconductivity.

DOI： 10.1103/PhysRevB.53.R14737

High-resolution photoemission study of CeRu2: The dual character of 4f electrons

Yang S. -H., Kumigashira H., Yokoya T., Chainani A., Takahashi T., Takeya H., Kadowaki K.

Physical review B 53 ( 18 ) R11946 - R11948 1996年5月

記述言語：英語出版者・発行元：American Physical Society

High-resolution low-temperature photoemission spectroscopy was performed for CeRu2 to study the nature of low-lying excitations around the Fermi level (EF). It was found that the photoemission spectrum near EF shows two well-resolved peaks at and about 270 meV below EF, which are ascribed to the tail of the Ce 4 f1 final state located just above EF and its spin-orbit satellite (ΔSO∼270 meV), respectively. This suggests that the many-body-correlation effect is necessary for understanding the electronic structure near EF of CeRu2, although the Ce 4f electron exhibits a substantially itinerant character through the strong hybridization with the conduction electrons.

DOI： 10.1103/PhysRevB.53.R11946

Extended van hove singularity in a noncuprate layered superconductor sr2RuO4

T. Yokoya, A. Chainani, T. Takahashi, H. Katayama-Yoshida, M. Kasai, Y. Tokura

Physical Review Letters 76 ( 16 ) 3009 - 3012 1996年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

Angle-resolved photoemission spectroscopy was performed on a ruthenate superconductor Sr2RuO4(Tc∼1 K) which has the same crystal structure as La2CuO4, but with RuO2 layers replacing CuO2 layers. Sr2RuO4 shows an extended Van Hove singularity (VHS) at 20±2 meV below EF just like the cuprates, regardless of the character of the electronic states at EF. This suggests that the extended VHS is a general feature of a two-dimensional correlated d-electron metal. The observed Fermi surface is in contrast to local-density-approximation calculations. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevLett.76.3009

Dual Character of 5f Electrons in UPd 2Al 3 Observed by High-Resolution Photoemission Spectroscopy

Takahashi Takashi, Sato Noriaki, Yokoya Takayoshi, Chainani Ashish, Morimoto Takayuki, Komatsubara Takemi

Journal of the Physical Society of Japan 65 ( 1 ) 156 - 159 1996年1月

記述言語：英語出版者・発行元：社団法人日本物理学会

Comparative high-resolution temperature-dependent photoemission measurements were performed for UPd2Al3 and UPd3. The photoemission spectrum near E F of UPd2Al3 consists of a sharp peak at E F and a broad band at 0.5–1.0 eV binding energy, both features having U 5f character. The sharp feature at E F shows good agreement with a recent band structure calculation, while the broad band matches well with the U 5f-derived localized feature in UPd3, indicating the dual character of 5f electrons in UPd2Al3. The intensity of the broad band relative to the E F-peak increases with increasing temperature, suggesting that the localized character of 5f electrons in UPd2Al3 increases at higher temperatures. These observations are consistent with the transport and magnetic measurements which imply a temperature-dependent dual (itinerant and localized) character of U 5f electrons in UPd2Al3.

DOI： 10.1143/JPSJ.65.156

その他リンク： https://jlc.jst.go.jp/DN/JALC/00038017919?from=CiNii

"Anisotropy and Doping Dependence of Superconducting Gap in Bi₂Sr₂CaCuO₈" 査読

T.Yokoya, H.Ding, T.Takeuchi, J.C.Campuzano, M.Randeria, M.R.Norman, T.Moshiku, K.Kadowaki, 門脇, 和男

Advances in Superconductivity (IX) 133-137 1996年1月

Extended van-Hove singularity in non-cuprate layered perovskite superconductor Sr2RuO4 査読

T Takahashi, T Yokoya, A Chainani, H KatayamaYoshida, M Kasai, Y Tokura

SPECTROSCOPIC STUDIES OF SUPERCONDUCTORS, PTS A AND B 2696 507 - 512 1996年

ARPES studies of the superconducting gap in high temperature superconductors 査読

H Ding, MR Norman, J Giapintzakis, JC Campuzano, H Claus, H Wuhl, M Randeria, A Bellman, T Yokoya, T Takahashi, T Mochiku, K Kadowaki, DM Ginsberg

SPECTROSCOPIC STUDIES OF SUPERCONDUCTORS, PTS A AND B 2696 496 - 506 1996年

High-resolution photoemission study of C: The dual character of electrons

S. H. Yang, H. Kumigashira, T. Yokoya, A. Chainani, T. Takahashi, H. Takeya

Physical Review B - Condensed Matter and Materials Physics 53 ( 18 ) R11946 - R11948 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

High-resolution low-temperature photoemission spectroscopy was performed for Ce(Formula presented) to study the nature of low-lying excitations around the Fermi level ((Formula presented)). It was found that the photoemission spectrum near (Formula presented) shows two well-resolved peaks at and about 270 meV below (Formula presented), which are ascribed to the tail of the Ce 4 (Formula presented) final state located just above (Formula presented) and its spin-orbit satellite ((Formula presented) meV), respectively. This suggests that the many-body-correlation effect is necessary for understanding the electronic structure near (Formula presented) of Ce(Formula presented), although the Ce (Formula presented) electron exhibits a substantially itinerant character through the strong hybridization with the conduction electrons. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.R11946

High-energy-resolution photoemission study of and

H. Kumigashira, A. Chainani, T. Yokoya, O. Akaki, T. Takahashi, M. Ito, M. Kasaya, O. Sakai

Physical Review B - Condensed Matter and Materials Physics 53 ( 5 ) 2565 - 2568 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

We studied the electronic structure of isostructural (Formula presented) and (Formula presented) using high-resolution low-temperature photoemission spectroscopy. (Formula presented) is a typical valence fluctuation material, while (Formula presented) is a low (Formula presented)(∼10 K) heavy-fermion system. The valence-band spectra show that Ni 3d derived states appear at energies closer to the Fermi level ((Formula presented)) compared to the Pt 5d derived states. The near-(Formula presented) spectra exhibit the characteristic spin-orbit splitting of 4f states (4(Formula presented) and 4(Formula presented)), with higher 4(Formula presented) intensity in (Formula presented) than in (Formula presented). Numerical simulations based on the single-impurity Anderson model show that the hybridization between the conduction band and f electrons is stronger in (Formula presented) than in (Formula presented). This is qualitatively understood in terms of proximity of Ni 3d states to the f level. The obtained spectroscopic results were discussed in comparison with transport and magnetic measurements. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.2565

Cooperative effects of electron correlation and charge ordering on the metal-insulator transition in quasi-one-dimensional deuteratedCu

T. Takahashi, T. Yokoya, A. Chainani, H. Kumigashira, O. Akaki, R. Kato

Physical Review B - Condensed Matter and Materials Physics 53 ( 4 ) 1790 - 1794 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

We study the changes in the electronic structure of a quasi-one-dimensional organic conductor, deuterated (Formula presented)Cu, across the CDW/M-I (charge-density-wave/metal-insulator) transition at (Formula presented) K, using temperature-dependent (30-300 K) high-resolution photoemission spectroscopy. Above the mean-field (MF) transition temperature ((Formula presented)), the system shows typical metallic behavior with small but finite density of states at (Formula presented). The spectral weight in the vicinity of (Formula presented) decreases systematically upon decreasing temperature below (Formula presented) even in the metallic phase, resulting in a pseudogap formation above (Formula presented). This behavior continues across (Formula presented) and causes the M-I transition. The spectral weight is transferred to energies much larger than the gap, indicating a cooperative effect of strong electron correlation and structural changes which imply decreases in interchain coupling across the M-I transition. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.1790

Evidence for correlation effects i from resonant and x-ray photoemission spectroscopy

T. Yokoya, A. Chainani, T. Takahashi, H. Katayama-Yoshida, M. Kasai, Y. Tokura

Physical Review B - Condensed Matter and Materials Physics 53 ( 13 ) 8151 - 8154 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

We study the electronic structure of (Formula presented)(Formula presented), a noncuprate layered superconductor ((Formula presented)=0.93 K), using electron spectroscopy. X-ray photoemission spectroscopy shows that the single particle occupied density of states (DOS) is in fair agreement with the calculated DOS. However, resonant photoemission spectroscopy across the Ru 4p-4d threshold establishes the existence of a correlation satellite to the Ru 4d band. The results indicate substantial charge-transfer character at the Fermi level, with on-site correlations (Formula presented) comparable in magnitude to the Ru-O hopping integral, like the cuprates. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.8151

High-resolution angle-resolved photoemission spectroscopy of CeBi

H. Kumigashira, S. Yang, T. Yokoya, A. Chainani, T. Takahashi, A. Uesawa, T. Suzuki, O. Sakai, Y. Kaneta

Physical Review B - Condensed Matter and Materials Physics 54 ( 13 ) 9341 - 9345 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

High-resolution angle-resolved photoemission spectroscopy (HR-ARPES) has been performed on a CeBi single crystal to study the complicated electronic structure near the Fermi level ((Formula presented)). The experimental result was compared with the band-structure calculation based on the p-f mixing model as well as the de Haas-van Alphen (dHvA) effect measurements. It was found that the overall feature of the valence band shows a remarkably good agreement between the experiment and the calculation, suggesting the essential validity of the p-f mixing model. HR-ARPES measurement near (Formula presented) has established the existence of a small electron pocket centered at the M point in the Brillouin zone, supporting the band calculation and the dHvA measurement. HR-ARPES spectra around the Γ point show some dispersive bands near (Formula presented) indicative of a hole pocket centered at the Γ point, though it was not so clearly resolved as the electron pocket due to close proximity of individual bands. These results are consistent with the semimetallic nature of CeBi. The observed quantitative discrepancy between the experiment and the calculation is discussed. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.54.9341

High-resolution angle-resolved photoemission spectroscopy of the momentum dependence of the superconducting gap i

T. Yokoya, T. Takahashi, T. Mochiku, K. Kadowaki

Physical Review B - Condensed Matter and Materials Physics 53 ( 21 ) 14055 - 14057 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）

The momentum dependence of the superconducting gap in (Formula presented)(Formula presented)Ca(Formula presented)(Formula presented) has been studied using high-resolution angle-resolved photoemission spectroscopy with nonpolarized light. The size of the superconducting gap obtained at several points on the Fermi surface shows a linear dependence with respect to the gap function of the (Formula presented) wave defined as (Formula presented). This suggests that the anomaly in the superconducting gap observed with polarized synchrotron-radiation light is not intrinsic, being probably due to the superstructure of the BiO plane, and rather the strong anisotropy of the superconducting gap, like the (Formula presented) symmetry, is intrinsic. © 1996 The American Physical Society.

DOI： 10.1103/PhysRevB.53.14055

Extended van-Hove singularity in Sr2RuO4 observed by angle-resolved photoemission

T. Yokoya, A. Chainani, T. Takahashi, H. Katayama-Yoshida, M. Kasai, Y. Tokura

Physica C: Superconductivity and its Applications 263 ( 1-4 ) 505 - 509 1996年

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier

We have performed low-temperature high-resolution angle-resolved photoemission spectroscopy on a non-cuprate superconductor Sr2RuO4 (Tc ∼ 1 K) which has the same crystal structure as La2CuO4 but with RuO2 layers replacing CuO2. We found that Sr2RuO4 has an extended van-Hove singularity (VHS) close to EF(20 ± 2 meV) like high-Tc cuprates, regardless of the character of the electronic states at EF, suggesting that the extended VHS is a general feature of a two-dimensional d-electron metal. This demands re-examination of the VHS scenario for the superconducting properties of cuprates, while T-linear resistivity seems to be consistent with this result.

DOI： 10.1016/0921-4534(96)00073-1

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