Faculty Profiles - YOKOYA Takayoshi

Papers - YOKOYA Takayoshi

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Superconducting gap anisotropy and quasiparticle interactions: A doping dependent photoemission study

J. Mesot, M. R. Norman, H. Ding, M. Randeria, J. C. Campuzano, A. Paramekanti, H. M. Fretwell, A. Kaminski, T. Takeuchi, T. Yokoya, T. Sato, T. Takahashi, T. Mochiku, K. Kadowaki

Physical Review Letters 83 ( 4 ) 840 - 843 1999.1

Language：English Publishing type：Research paper (scientific journal)

Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d-wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple coskx−cosky form, which suggests an increasing importance of long range interactions as the insulator is approached. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevLett.83.840

Angle-resolved photoemission study of Sr2CuO3

H. Fujisawa, T. Yokoya, T. Takahashi, S. Miyasaka, M. Kibune, H. Takagi

Physical Review B - Condensed Matter and Materials Physics 59 ( 11 ) 7358 - 7361 1999

Language：English Publishing type：Research paper (scientific journal)

We report angle-resolved photoemission spectroscopy (ARPES) on a single Cu-O chain compound Sr2CuO3 with Ne I photons. In contrast with previous ARPES with higher-energy photons, the present result clearly shows two well-separated branches of dispersions near EF ascribable to spinon and holon excitations, respectively. This indicates that spin and charge degrees of freedom are separated in one-dimensional Cu-O chains, supporting the theoretical prediction as well as the previous ARPES interpretation. Comparison with previous ARPES results indicates that surface, photoionization cross section, and finite-temperature effects substantially modify ARPES spectra. © 1999 ThAmerican Physical Society.

DOI： 10.1103/PhysRevB.59.7358

BSCCO superconductors : Hole-like Fermi surface and doping dependence of the gap function(共著)

J. Mesot, M. R. Norman, H. Ding, M. Randeria, J. C. Campuzano, A. Paramekanti, H. M. Fretwell, A. Kaminski, T. Takeuchi, T. Yokoya, T. Sato, T. Takahashi, T. Mochiku, K. Kadowaki

JOURNAL OF LOW TEMPERATURE PHYSICS 117 ( 3-4 ) 365 - 369 1999

Publishing type：Research paper (scientific journal)

We use the gradient of the energy-integrated angle resolved photoemission (ARPES) intensity in order to define precisely the Fermi surface (FS) in BSCCO superconductors. We show that, independent of the photon energy, the FS is a hole barrel centered at (π, π). Then, the superconducting gap along the FS is precisely determined from ARPES measurements on overdoped and underdoped samples of Bi2212. As the doping decreases, the maximum gap increases, but the slope of the gap near the nodes decreases. Though consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple cos(k ) - cos(k ) form. A comparison of our ARPES results with available penetration depth data indicates that the renormalization of the linear T suppression of the superfluid density at low temperatures due to quasiparticle excitations around the d-wave nodes is large and doping dependent. x y

DOI： 10.1023/A:1022569616840

Electronic structure of (formula presented) comparison between substitutional and vacancy doping

T. Yokoya, T. Sato, H. Fujisawa, T. Takahashi, A. Chainani, M. Onoda

Physical Review B - Condensed Matter and Materials Physics 59 ( 3 ) 1815 - 1818 1999

Language：English Publishing type：Research paper (scientific journal)

The change of the electronic structure across the metal-insulator transition in a Mott-Hubbard system (Formula presented) has been investigated by x-ray absorption and photoemission spectroscopy. The results are compared with (Formula presented) where hole doping is achieved by excess oxygen instead of Sr substitution. It is found that additional doped-hole states are created in the insulator gap for both cases, while the density of states at the Fermi level in (Formula presented) is nearly half of that in (Formula presented) at the same nominal doping. This suggests a strong reduction in the mobility of carriers due to cation vacancies produced by excess oxygen. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevB.59.1815

Metallic-covalent bonding conversion in Alminum-based and Boron-based icosahedral cluster solids Reviewed

K. Kimura, H. Matsuda, M. Fujimori, M. Terauchi, M. Tanaka, H. Kumigashira, T. Yokoya, T. Takahashi

Proc. 6th Int. Conf. Quasicrystals 595 - 598 1998.12

Destruction of the Fermi surface in underdoped high-T(c) superconductors

M. R. Norman, H. Ding, M. Randeria, J. C. Campuzano, T. Yokoya, T. Takeuchi, T. Takahashi, T. Mochiku, K. Kadowaki, P. Guptasarma, D. G. Hinks

Nature 392 ( 6672 ) 157 - 160 1998.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Macmillan Magazines Ltd

The Fermi surface - the set of points in momentum space describing gapless electronic excitations - is a central concept in the theory of metals. In this context, the normal 'metallic' state of the optimally doped high-temperature superconductors is not very unusual: above the superconducting transition temperature, T(c), there is evidence for a large Fermi surface1-3 despite the absence of well-defined elementary excitations. In contrast, the normal state of underdoped high-temperature superconductors differs in that there is evidence for a 'pseudogap' above T(c) (refs 4-6). Here we examine, using angle-resolved photoemission spectroscopy, the temperature dependence of the Fermi surface in underdoped Bi2Sr2CaCu2O(8+δ). We find that, on cooling the sample, the pseudo-gap opens up at different temperatures for different points in momentum space. This leads to an initial breakup of the Fermi surface, at a temperature T*, into disconnected arcs, which then shrink with decreasing temperature before collapsing to the point nodes of the superconducting ground state below T(c). This unusual behaviour, where the Fermi surface does not form a continuous contour in momentum space as in conventional metals, is unprecedented in that it occurs in the absence of long-range order. Moreover, although the superconducting gap below T(c) evolves smoothly into the pseudogap above T(c), the pseudogap differs in its unusual temperature-dependent anisotropy, implying an intimate but non-trivial relationship between the pseudo-gap and the superconducting gap.

DOI： 10.1038/32366

Spin-charge separation in single-chain compound Sr2CuO3 studied by angle-resolved photoemission

H. Fujisawa, T. Yokoya, T. Takahashi, S. Miyasaka, M. Kibune, H. Takagi

Solid State Communications 106 ( 8 ) 543 - 547 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

Angle-resolved photoemission measurements were performed for one-dimensional Sr2CuO3 which consists of single Cu-O chains. Two dispersive bands were observed near EF in the first half of the Brillouin zone (k = 0 to π/2) of the chain-direction. Both bands have a common maximum point closest to EF at k = π/2 while they show different dispersions of about 0.25 and 1 eV, respectively, with a continuous intensity distribution in between. The less dispersive band is almost diminished in another half of the Brillouin zone (k = π/2 to π). These results are consistent with the solution of the one-dimensional Hubbard model as well as the t-J model calculation, suggesting the spin-charge separation in the one-dimensional Cu-O chain. The experimental results are compared with those of the double-chain compound SrCuO2. © 1998 Published by Elsevier Science Ltd.

DOI： 10.1016/S0038-1098(98)00099-4

Angle-resolved photoemission study of superconducting ladder compound Sr14-xCaxCu24O41

T. Sato, T. Yokoya, T. Takahashi, M. Uehara, T. Nagata, J. Goto, J. Akimitsu

Journal of Physics and Chemistry of Solids 59 ( 10-12 ) 1912 - 1916 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

Angle-resolved photoemission spectroscopy has been performed on Sr14-xCaxCu24O41 (x = 0-11.5) which consists of two-leg Cu2O3 ladders and edge-sharing CuO2 chains. A dispersive band with the periodicity of ladder sublattice is observed near the Fermi level (EF) for x=0. The band shows a minimum binding energy at ka= (2n + 1)π/2, suggesting that a Mott-Hubbard gap opens on the ladder. This indicates that copper atoms on the ladder take essentially the divalent state (Cu2+) and a majority of self-doped holes reside on the chain. We found that the Ca substitution causes a transfer of holes from the chain to the ladder. © 1998 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(98)00148-6

Magnetic phase transition of CeSb studied by high-resolution angle-resolved photoemission

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

Journal of Magnetism and Magnetic Materials 177-181 ( 2 ) 1027 - 1028 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier

We observed a change of Fermi-surface topology of CeSb across the magnetic phase transition using temperature-dependent high-resolution angle-resolved photoemission spectroscopy. The experimental results show that the complicated magnetic structure of CeSb strongly relates to its unique electronic structure as predicted by the anisotropic p-f mixing model. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00440-X

Arpes study of the superconducting gap and pseudogap in Bi2Sr2CaCu2O8+x

H. Ding, J. C. Campuzano, M. R. Norman, M. Randeria, T. Yokoya, T. Takahashi, T. Takeuchi, T. Mochiku, K. Kadowaki, P. Guptasarma, D. G. Hinks

Journal of Physics and Chemistry of Solids 59 ( 10-12 ) 1888 - 1891 1998

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Ltd

In this paper, we review some of our ARPES results on the superconducting and pseudo gaps in Bi2Sr2CaCu2O8+x. We find that optimally and overdoped samples exhibit a d-wave gap, which closes at the same temperature, Tc, for all k points. In underdoped samples, a leading edge gap is found up to a temperature T* &gt
Tc. We find that T* scales with the maximum low temperature gap, increasing as the doping is reduced. The momentum dependence of the pseudogap is similar to that of the superconducting gap
however, the pseudogap closes at different temperatures for different k points. © 1998 Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(98)00136-X

Unusual dispersion and line shape of the superconducting state spectra of Bi2Sr2CaCu2O8 + δ

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

Physical Review Letters 79 ( 18 ) 3506 - 3509 1997.11

Language：English Publishing type：Research paper (scientific journal)

Photoemission spectra of Bi2Sr2CaCu2O8 + δ below Tc show two features near the (π, 0) point of the zone: a sharp peak at low energy and a higher binding energy hump. We find that the sharp peak persists at low energy even as one moves towards (0, 0), while the broad hump shows significant dispersion which correlates well with the normal state dispersion. We argue that these features are naturally explained by the interaction of electrons with a sharp mode which appears only below Tc, and speculate that the latter may be related to the resonance seen in recent neutron data. © 1997 American Physical Society.

DOI： 10.1103/PhysRevLett.79.3506

Evolution of the fermi surface with carrier concentration in Bi2Sr2CaCu2O8+δ

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

Physical Review Letters 78 ( 13 ) 2628 - 2631 1997.3

Language：English Publishing type：Research paper (scientific journal)

We show, by use of angle-resolved photoemission spectroscopy, that underdoped Bi2Sr2CaCu2O8+δ appears to have a large Fermi surface centered at (π, π), even for samples with a Tc as low as 15 K. No clear evidence of a Fermi surface pocket around (π/2, π/2) has been found. These conclusions are based on a determination of the minimum gap locus in the pseudogap regime Tc &lt
T &lt
T*, which is found to coincide with the locus of gapless excitations in momentum space (Fermi surface) determined above T* . These results suggest that the pseudogap is more likely of precursor pairing rather than magnetic origin. © 1997 American Physical Society.

DOI： 10.1103/PhysRevLett.78.2628

Extended Van Hove singularity in a noncuprate layered superconductor Sr2RuO4 - Reply Reviewed

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

PHYSICAL REVIEW LETTERS 78 ( 11 ) 2272 - 2272 1997.3

Comment on “extended van hove singularity in a noncuprate layered superconductor Sr2RuO4”

A. P. Mackenzie, S. R. Julian, G. G. Lonzarich, Y. Maeno, T. Fujita

Physical Review Letters 78 ( 11 ) 2271 1997

Angle-resolved photoemission study of Sr2RuO4; An extended van-Hove singularity in non-cuprate superconductor

T. Takahashi, T. Yokoya, A. Chainani, H. Ding, J. C. Campuzano, M. Kasai, Y. Tokura

Physica C: Superconductivity and its Applications 282-287 ( 1 ) 218 - 221 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier

We have performed high-resolution angle-resolved photoemission spectroscopy of a non-cuprate layered superconductor Sr2RuO4 to study the electronic structure near the Fermi level (EF). The result shows an extended van Hove singularity (vHs) along the Ru-O bonding direction just like the cuprate, regardless of the character of the electronic states at EF. This suggests that the extended vHs is a general electronic structure of a two dimensional correlated d-electron metal. We also have found that the observed Fermi surface topology (one electron-like Fermi surface sheet centered at Γ point and two hole-like ones centered at X point) is qualitatively different from the calculated Fermi surface topology (two electron-like Fermi sheets centered at Γ point and one hole-like one centered at X point) in the consequence of the existence of the vHs.

DOI： 10.1016/S0921-4534(97)00208-6

Electronic Band Structure of SrCuO2

Naoyuki Nagasako, Tamio Oguchi, Hideki Fujisawa, Osamu Akaki, Takayoshi Yokoya, Takashi Takahashi, Masayuki Tanaka, Masashi Hasegawa, Humihiko Takei

Journal of the Physical Society of Japan 66 ( 6 ) 1756 - 1761 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：Physical Society of Japan

The energy band structure of a quasi one-dimensional cuprate SrCuO2 is studied by angle-resolved photoemission spectroscopy and the linear augmented-plane-wave band structure calculation within local density approximation. It was found that the band structure has strongly one-dimensional nature with a finite dispersion along the Cu-O chains. The calculated band structure of SrCuO2 is in good agreement with the angle-resolved photoemission result except for the region near the Fermi level.

DOI： 10.1143/JPSJ.66.1756

Unconventional spectral changes across the metal-insulator transition

O. Akaki, A. Chainani, T. Yokoya, H. Fujisawa, T. Takahashi, M. Onoda

Physical Review B - Condensed Matter and Materials Physics 56 ( 19 ) 12050 - 12053 1997

Language：English Publishing type：Research paper (scientific journal)

We study the change in the electronic structure of (Formula presented) across the δ-controlled metal-insulator (M-I) transition. X-ray-absorption spectroscopy shows the formation of hole states with substantial (Formula presented) character as a function of δ. Ultraviolet photoemission spectroscopy confirms the gap (Formula presented) closure across the M-I transition due to the doped hole states. The results show that a Mott-Hubbard system can have a charge-transfer character due to the strong hybridization, indicating a very mixed character ground state. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.56.12050

ARPES studies of Pb substituted Bi2201 compounds

T. Takeuchi, H. Ding, J. C. Campuzano, T. Yokoya, T. Takahashi, I. Chong, T. Terashima, M. Takano

Physica C: Superconductivity and its Applications 282-287 ( 2 ) 999 - 1000 1997

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier

We report angle-resolved photoemission of overdoped Bi1.80Pb0.38Sr2.01CuO6 with different Tc's of 4, 8, and 20 K. All samples show similar large Fermi surfaces, centered at (π, π). However, the spectral function linewidth decreases as doping increases. The 4K sample is found to have the typical Fermi liquid linewidth. Comparison is also made to the two layer Bi2Sr2CaCu2O8 compound.

DOI： 10.1016/S0921-4534(97)00572-8

Angle-resolved photoemission study of the ladder compound

T. Takahashi, T. Yokoya, A. Ashihara, O. Akaki, H. Fujisawa, A. Chainani, M. Uehara, T. Nagata, J. Akimitsu

Physical Review B - Condensed Matter and Materials Physics 56 ( 13 ) 7870 - 7873 1997

Language：English Publishing type：Research paper (scientific journal)

Angle-resolved photoemission measurements have been performed on (Formula presented) which consists of two-leg (Formula presented) ladders and edge-sharing (Formula presented) chains. The data are consistent with the existence of a dispersive band near the Fermi level which has the periodicity of the ladder sublattice. The band shows a minimum binding energy at (Formula presented) suggesting that a Mott-Hubbard gap opens on the ladder. The experimental result shows a qualitative agreement with the (Formula presented) ladder calculation. It was also found that replacement of Sr with Ca causes a transfer of holes from the chain to the ladder. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.56.7870

High-resolution temperature-dependent valence-band photoemission spectroscopy of gold:mNature of electron-phonon coupling

T. Yokoya, A. Chainani, T. Takahashi

Physical Review B - Condensed Matter and Materials Physics 55 ( 9 ) 5574 - 5577 1997

Language：English Publishing type：Research paper (scientific journal)

Using high-resolution temperature-dependent (20-400 K) valence-band photoemission spectroscopy, we study the nature of electron-phonon coupling in polycrystalline gold. The valence band shows systematic broadening for increasing temperatures which is well-reproduced by a Gaussian broadening of the 20 K spectrum. It depends linearly on temperature and is found to be excessive (∼9 (Formula presented) T). The results suggest the existence of anharmonic lattice vibrations and a quadratic electron-phonon coupling, similar to the case of aluminum 2p core levels. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.55.5574

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