Faculty Profiles - YOKOYA Takayoshi

Papers - YOKOYA Takayoshi

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Carbon-substitution dependent multiple superconducting gap of MgB2: A sub-meV resolution photoemission study Reviewed

S Tsuda, T Yokoya, T Kiss, T Shimojima, S Shin, T Togashi, S Watanabe, C Zhang, CT Chen, S Lee, H Uchiyama, S Tajima, N Nakai, K Machida

PHYSICAL REVIEW B 72 ( 6 ) 2005.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

"Sub-meV" resolution photoemission spectroscopy was used to study carbon-substitution dependence of the multiple superconducting gap of Mg(B1-xCx)(2). Two features corresponding to sigma and pi gaps are clearly observed in the raw spectra up to carbon concentration x=0.075. The observed x dependence of the two gaps shows a qualitatively different behavior: the sigma gap is proportional to T-c while the pi gap shows negligible change. Doping as well as temperature dependence can be explained within the two-band mean-field theory. Implications from the present study are discussed.

DOI： 10.1103/PhysRevB.72.064527

Hard-X-ray photoelectron spectroscopy of NaxCoO2 center dot yH(2)O Reviewed

A Chainani, T Yokoya, Y Takata, K Tamasaku, M Taguchi, T Shimojima, N Kamakura, K Horiba, S Tsuda, S Shin, D Miwa, Y Nishino, T Ishikawa, M Yabashi, K Kobayashi, H Namatame, M Taniguchi, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 547 ( 1 ) 163 - 168 2005.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We study the bulk electronic structure of Na(x)CoO(2 center dot)yH(2)O using Hard X-ray (HX, hv = 5.95KeV) synchrotron photoelectron spectroscopy (PES). The Co 2p core level spectra show well-separated Co3+ and Co4+ ions. Cluster calculations suggest low spin Co3+ and Co4+ character, and a moderate on-site Coulomb correlation energy U-dd similar to 3-5.5 eV. Photon-dependent valence band PES identifies Co 3d and 0 2p derived states, in near agreement with band structure calculations. We discuss the importance of HX-PES for studying correlated transition metal oxides. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.nima.2005.05.021

Contribution of electronic structure to thermoelectric power in (Bi,Pb)(2)(Sr,La)(2)CuO6+delta Reviewed

T Kondo, T Takeuchi, U Mizutani, T Yokoya, S Tsuda, S Shin

PHYSICAL REVIEW B 72 ( 2 ) 2005.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

The energy-momentum (epsilon-k) dispersion and the shape of the Fermi surface in the (Bi,Pb)(2)(Sr,La)(2)CuO6+delta (Bi2201) superconductors with various hole concentrations were determined by the high resolution angle-resolved photoemission spectroscopy. On the basis of the epsilon-k dispersion thus obtained, temperature and hole-concentration dependence of the thermoelectric power S(T) was calculated within the framework of the Boltzmann transport theory. S(T) of the optimally and overdoped samples was quantitatively reproduced by the present calculation, strongly indicating that characteristics in S(T) of the high-T-c cuprates under the optimally to overdoped conditions is unambiguously caused by the band structure characterized by the van Hove singularity near the Fermi level.

DOI： 10.1103/PhysRevB.72.024533

Hole-concentration dependence of electrical resistivity in the (Bi, Pb)(2)(Sr, La)(2)CuO6+delta quantitative evaluation with angle-resolved photoemission spectroscopy Reviewed

T Kondo, T Takeuchi, T Yokoya, S Tsuda, S Shin, U Mizutani

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 144 1249 - 1252 2005.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Relaxation time of Bloch states at the Fermi level (4), Fermi velocity (110, and mean free path (IF) of the conduction electrons in the (Bi, Pb)(2)(Sr, La)(2)CuO6+delta (Bi2201) superconductors with various hole-concentration (p) were determined by the angle-resolved photoemission spectroscopy (ARPES) measurement with high energy- and momentum-resolutions; Delta E = 10 meV and Delta k = 0.005 angstrom(-1). We found that tau(F) at k(F) along (0, 0)-(pi, pi) cut is kept constant over a wide Hole-concentration range while it in the vicinity of (pi, 0) is drastically shortened with decreasing p and eventually reaches nearly zero in the under-doped sample with the transition temperature of 27 K. By calculating electrical resistivity and comparing it with the measured one, we confirmed that tau(F), v(F), and l(F) determined by the ARPES measurement can be used for the quantitative estimation of the electrical transport properties, such as the electrical resistivity, in high-T-c cuprates. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2005.01.198

Ultrahigh-resolution photoemission spectroscopy of superconductors using a VUV laser Reviewed

T Kiss, T Shimojima, F Kanetaka, K Kanai, T Yokoya, S Shin, Y Onuki, T Togashi, CQ Zhang, CT Chen, S Watanabe

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 144 953 - 956 2005.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We have developed an ultrahigh-resolution photoemission system using a quasi continuous wave (quasi-CW) VUV laser. The photon energy of the VUV laser is 6.994 eV. It has a line width of 260 mu eV and a repetition rate of 80 MHz. The photon energy of this laser is the highest for a quasi-CW laser. Using a quasi-CW laser removes the space charge effect and hence does not degrade the energy resolution. For the electron analyser, we use the newly designed ultrahigh-resolution photoelectron analyser GAMMADATA-SCIENTA R4000. The analyser resolution is about 250 mu eV with a wide collecting angle of about 38 degrees. The total energy resolution of this system is measured to be 360 mu eV for the Fermi edge of gold. Using this system, we have measured several low transition temperature superconductors and succeeded to observe the bulk superconducting state of these materials. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2005.01.154

Role of charge-density-wave fluctuations on the spectral function in a metallic charge-density-wave system Reviewed

T Yokoya, T Kiss, A Chainani, S Shin, K Yamaya

PHYSICAL REVIEW B 71 ( 14 ) 2005.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

Angle-resolved photoemission spectroscopy of ZrTe3 has been performed from room temperature (T) down to 6 K (across T-CDW=63 K) to study the charge-density-wave (CDW) fluctuation effects in a metallic CDW compound having Fermi surface (FS) sheets with differing dimensionality. While spectra on the three-dimensional (3D) FS show typical Fermi-Dirac functionlike T dependence, those along the quasi-one-dimensional (1D) FS show formation of a pseudogap, starting at a much higher T than T-CDW. Simultaneously, a van-Hove singularity consisting of the quasi-1D FS intersecting the 3D FS shows an increase of coherence. This demonstrates the role of CDW fluctuations on the spectral function, and relation to the dimensionality of the states, in a metallic CDW system.

DOI： 10.1103/PhysRevB.71.140504

Bulk screening in core-level photoemission from Mott-Hubbard and charge-transfer systems Reviewed

M Taguchi, A Chainani, N Kamakura, K Horiba, Y Takata, M Yabashi, K Tamasaku, Y Nishino, D Miwa, T Ishikawa, S Shin, E Ikenaga, T Yokoya, K Kobayashi, T Mochiku, K Hirata, K Motoya

PHYSICAL REVIEW B 71 ( 15 ) 2005.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

We report bulk-sensitive hard x-ray (h nu=5.95 keV) core-level photoemission spectroscopy (PES) of single crystal V1.98Cr0.02O3 and the high-T-c cuprate Bi2Sr2CaCu2O8+delta (Bi2212). V1.98Cr0.02O3 exhibits low binding energy "satellites" to the V 2p "main lines" in the metallic phase, which are suppressed in the antiferromagnetic insulator phase. In contrast, the Cu 2p spectra of Bi2212 do not show temperature-dependent features, but a comparison with soft x-ray PES indicates a large increase in the 2p(5)3d(9) satellites or 3d(9) weight in the bulk. Cluster model calculations, including a full multiplet structure and a screening channel derived from the coherent band at the Fermi energy, give very satisfactory agreement with the experiments.

DOI： 10.1103/PhysRevB.71.155102

Absence of strong correlation in Li 2Pd 3B Reviewed

T. Yokoya, T. Muro, I. Hase, H. Takeya, K. Hirata, K. Togano

Physical Review B - Condensed Matter and Materials Physics 71 ( 9 ) 2005.3

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

We use x-ray photoemission spectroscopy to study the electronic structure of new superconductor Li 2Pd 3B. Binding energies of the Pd 3p and 3d indicate valency that is intermediate between Pd metal (0±) and PdO(2+), or effectively Pd 4d 9 configuration. Comparison of satellite features in core level spectra of Li 2Pd 3B with that of PdO suggests that a larger hybridization strength of Li 2Pd 3B than that of PdO. The valence band spectrum is in excellent agreement with first principle band structure calculations, allowing us to ascribe the states at the Fermi level responsible for the superconductivity to be mainly Pd 4d hybridized with B 2p and Li 2p. These observations indicate that correlation effects play a negligible role for the physical properties of the new superconductor. ©2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.092507

Absence of strong correlation in Li2Pd3B Reviewed

T Yokoya, T Muro, Hase, I, H Takeya, K Hirata, K Togano

PHYSICAL REVIEW B 71 ( 9 ) 2005.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We use x-ray photoemission spectroscopy to study the electronic structure of new superconductor Li2Pd3B. Binding energies of the Pd 3p and 3d indicate valency that is intermediate between Pd metal (0) and PdO(2+), or effectively Pd 4d(9) configuration. Comparison of satellite features in core level spectra of Li2Pd3B with that of PdO suggests that a larger hybridization strength of Li2Pd3B than that of PdO. The valence band spectrum is in excellent agreement with first principle band structure calculations, allowing us to ascribe the states at the Fermi ,level responsible for the superconductivity to be mainly Pd 4d hybridized with B 2p and Li 2p. These observations indicate that correlation effects play a negligible role for the physical properties of the new superconductor.

DOI： 10.1103/PhysRevB.71.092507

Photoemission spectroscopic evidence of gap anisotropy in an f-electron superconductor Reviewed

T Kiss, F Kanetaka, T Yokoya, T Shimojima, K Kanai, S Shin, Y Onuki, T Togashi, C Zhang, CT Chen, S Watanabe

PHYSICAL REVIEW LETTERS 94 ( 5 ) 2005.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

We used low-temperature ultrahigh-resolution (360 mueV) photoemission spectroscopy with a laser as a photon source (Laser-PES) to study the superconducting (SC) gap of an f-electron superconductor CeRu2. The unique combination of the large escape depth expected from the known universal behavior and extremely high-energy resolution has enabled us to directly measure the bulk SC gap of an f-electron superconductor for the first time. The present study provides direct evidence for an anisotropic SC gap in CeRu2, and also demonstrates the potential of Laser-PES in investigating unconventional superconductivity realized in correlated d- and f-electron superconductors.

DOI： 10.1103/PhysRevLett.94.057001

Laser-excited ultrahigh-resolution photoemission spectroscopy of NaxCoO2 center dot yH(2)O: Evidence for pseudogap formation Reviewed

T Shimojima, T Yokoya, T Kiss, A Chainani, S Shin, T Togashi, S Watanabe, C Zhang, CT Chen, K Takada, T Sasaki, H Sakurai, E Takayama-Muromachi

PHYSICAL REVIEW B 71 ( 2 ) 2005.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We have studied the temperature (T)-dependent electronic structure near the Fermi level of the layered cobaltate superconductor, Na0.35CoO2.1.3H(2)O, and related materials, using laser-excited ultrahigh-resolution photoemission spectroscopy. We observe the formation of a pseudogap (PG) with an energy scale of similar to20 meV in Na0.35CoO2.1.3H(2)O and Na0.35CoO2.0.7H(2)O, which is clearly absent in Na0.7CoO2. The energy scale of the PG is larger than the expected value for the superconducting gap, suggesting an additional competing order parameter at low T. We discuss implications of the PG in relation to available transport and magnetic susceptibility results.

DOI： 10.1103/PhysRevB.71.020505

Laser-excited ultrahigh-resolution photoemission spectroscopy of Na xCoO 2·yH 2O: Evidence for pseudogap formation Reviewed

T. Shimojima, T. Yokoya, T. Kiss, A. Chainani, S. Shin, T. Togashi, S. Watanabe, C. Zhang, C. T. Chen, K. Takada, T. Sasaki, H. Sakurai, E. Takayama-Muromachi

Physical Review B - Condensed Matter and Materials Physics 71 ( 2 ) 2005.1

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

We have studied the temperature (T)-dependent electronic structure near the Fermi level of the layered cobaltate superconductor, Na 0.35CoO 2·1.3H 2O, and related materials, using laser-excited ultrahigh-resolution photoemission spectroscopy. We observe the formation of a pseudogap (PG) with an energy scale of ∼20 meV in Na 0.35CoO 2·1.3H 2O and Na 0.35CoO 2·0.7H 2O, which is clearly absent in Na 0.7CoO 2. The energy scale of the PG is larger than the expected value for the superconducting gap, suggesting an additional competing order parameter at low T. We discuss implications of the PG in relation to available transport and magnetic susceptibility results. ©2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.020505

Electronic structure changes across the valence transition in EuNi <inf>2</inf>(Si<inf>0.2</inf>Ge<inf>0.8</inf>)<inf>2</inf>

P. A. Rayjada, P. A. Rayjada, A. Chainani, A. Chainani, K. Kanai, K. Kanai, T. Haruna, T. Yokoya, S. Shin, S. Shin, H. Wada, M. Shiga

Physical Review B - Condensed Matter and Materials Physics 70 1 - 7 2004.12

We study the electronic structure of EuNi2(Si 0.2Ge0.8)2, which exhibits a temperature dependent mixed valence transition, using 4d-4f resonant photoemission spectroscopy (RESPES), x-ray absorption spectroscopy (XAS) and temperature-dependent ultraviolet photoemission spectroscopy (UPS). The RESPES studies identify the divalent and trivalent Eu 4f character density of states (DOS) which participate in the valence transition. Using the photoionization cross section variation as a function of photon energy, we discuss the Eu, Ni, and Ge-Si partial DOS in the valence band. The bulk divalent Eu 4f character states are centered at a binding energy of about 0.75 eV, significantly away from the Fermi level. While the surface divalent feature is negligibly affected, the spectra obtained using He IIα UPS exhibit temperature dependent bulk Eu 4f character states. The bulk divalent spectral weight is transferred to the high energy trivalent states, across the valence transition temperature, T υ ∼ 80 K. The He Iα UPS also exhibit spectral intensity changes across Tυ. The non-f character conduction band states at and near the Fermi level exhibit spectral weight changes up to 350 meV with a small energy (∼25 meV) temperature dependent pseudogaplike feature. The results suggest an increase in effective hybridization strength between the conduction and 4f electrons in the low temperature nearly trivalent phase. While the 4f character changes across Tυ are qualitatively consistent with change in valence configurations, the temperature dependent spectral changes in the non-f character DOS indicate direct participation in the valence transition in EuNi2(Si 0.2Ge0.8)2.

DOI： 10.1103/PhysRevB.70.235105

Electronic structure changes across the valence transition in EuNi2(Si0.2Ge0.8)(2) Reviewed

PA Rayjada, A Chainani, K Kanai, T Haruna, T Yokoya, S Shin, H Wada, M Shiga

PHYSICAL REVIEW B 70 ( 23 ) 2004.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We study the electronic structure of EuNi2(Si0.2Ge0.8)(2), which exhibits a temperature dependent mixed valence transition, using 4d-4f resonant photoemission spectroscopy (RESPES), x-ray absorption spectroscopy (XAS) and temperature-dependent ultraviolet photoemission spectroscopy (UPS). The RESPES studies identify the divalent and trivalent Eu 4f character density of states (DOS) which participate in the valence transition. Using the photoionization cross section variation as a function of photon energy, we discuss the Eu, Ni, and Ge-Si partial DOS in the valence band. The bulk divalent Eu 4f character states are centered at a binding energy of about 0.75 eV, significantly away from the Fermi level. While the surface divalent feature is negligibly affected, the spectra obtained using He IIalpha UPS exhibit temperature dependent bulk Eu 4f character states. The bulk divalent spectral weight is transferred to the high energy trivalent states, across the valence transition temperature, T(v)similar to80 K. The He Ialpha UPS also exhibit spectral intensity changes across T-v. The non-f character conduction band states at and near the Fermi level exhibit spectral weight changes up to 350 meV with a small energy (similar to25 meV) temperature dependent pseudogaplike feature. The results suggest an increase in effective hybridization strength between the conduction and 4f electrons in the low temperature nearly trivalent phase. While the 4f character changes across T-v are qualitatively consistent with change in valence configurations, the temperature dependent spectral changes in the non-f character DOS indicate direct participation in the valence transition in EuNi2(Si0.2Ge0.8)(2).

DOI： 10.1103/PhysRevB.70.235105

Valence-band photoemission study of beta-ZrNCl and the quasi-two-dimensional superconductor NaxZrNCl Reviewed

T Yokoya, T Takeuchi, S Tsuda, T Kiss, T Higuchi, S Shin, K Iizawa, S Shamoto, T Kajitani, T Takahashi

PHYSICAL REVIEW B 70 ( 19 ) 2004.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

We have performed photoemission (PE) spectroscopy of beta-ZrNCl and NaxZrNCl to study intercalation-induced change in the electronic structure. The valence band PE spectrum of beta-ZrNCl shows a small intensity region within similar to2.5 eV of E-F with a very small hump at E-F that can be ascribed to hydrogen impurity states. These provide spectroscopic evidence that beta-ZrNCl is an n-type semiconductor. Upon Na intercalation, new states possibly involving hybridized Zr4d and N2p systematically evolve at E-F, with a negligible shift in the valence band structures. Similar results in beta-HfNCl and NaxHfNCl indicate that these results represent common electronic features of the layered nitride chloride superconductors.

DOI： 10.1103/PhysRevB.70.193103

Valence-band photoemission study of β-ZrNCl and the quasi-two-dimensional superconductor NaxZrNCl Reviewed

T. Yokoya, T. Takeuchi, S. Tsuda, T. Kiss, T. Higuchi, S. Shin, K. Iizawa, S. Shamoto, T. Kajitani, T. Takahashi

Physical Review B - Condensed Matter and Materials Physics 70 ( 19 ) 1 - 4 2004.11

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

We have performed photoemission (PE) spectroscopy of β-ZrNCl and NaxZrNCl to study intercalation-induced change in the electronic structure. The valence band PE spectrum of β-ZrNCl shows a small intensity region within ∼2.5 eV of EF with a very small hump at E F that can be ascribed to hydrogen impurity states. These provide spectroscopic evidence that β-ZrNCl is an n-type semiconductor. Upon Na intercalation, new states possibly involving hybridized Zr4d and N2p systematically evolve at EF, with a negligible shift in the valence band structures. Similar results in β-HfNCl and NaxHfNCl indicate that these results represent common electronic features of the layered nitride chloride superconductors.

DOI： 10.1103/PhysRevB.70.193103

Electronic structure and superconducting gap of silicon clathrate Ba8Si46 studied with ultrahigh-resolution photoemission spectroscopy (vol B 64, art no 172504, 2001) Reviewed

T Yokoya, A Fukushima, T Kiss, K Kobayashi, S Shin, K Moriguchi, A Shintani, H Fukuoka, S Yamanaka

PHYSICAL REVIEW B 70 ( 15 ) 2004.10

The Fermi surface and sheet-dependent superconducting gap of MgB2 Reviewed

S Tsuda, T Yokoya, S Shin, Y Takano, H Kito, A Matsushita, F Yin, J Itoh, H Harima

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 412 36 - 40 2004.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The Fermi surface and superconducting gap of MgB2 have been studied by angle-resolved photoemission spectroscopy. Two Fermi surfaces composed of the a band and the pi band are clearly observed without contaminated by the "surface-derived" band. The high-resolution photoemission spectra show that superconducting gaps with values of 5.5 and 2.2 meV open on the sigma band and the pi band, respectively, both of which close at the bulk transition temperature (T-c). This result provides an experimental evidence for the two-band superconductivity on MgB2 and, moreover, validates the role of momentum-dependent electron-phonon coupling as the origin of multiple-gap superconductivity as well as the high transition temperature (T-c) of MgB2. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2004.01.037

Electronic structure and large thermoelectric power in Ca3Co4O9 Reviewed

T Takeuchi, T Kondo, K Soda, U Mizutani, R Funahashi, M Shikano, S Tsuda, T Yokoya, S Shin, T Muro

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 137 595 - 599 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Resonant photoemission spectroscopy, soft X-ray emission spectroscopy, soft X-ray absorption spectroscopy, and high-resolution (DeltaE approximate to 10 meV) ultraviolet photoemission spectroscopy were performed on a layered cobalt oxide, Ca3Co4O9, which has attracted interests as one of the potential thermoelectric materials because of its possession of high thermoelectric power S, relatively low electrical resistivity rho, and small thermal conductivity kappa. A narrow band of 1.5-2 eV in width was observed in the photoemission spectra with its center at 1.0 eV below the Fermi level (E-F). This peak turns out to be less significant when Co 2p-3d resonance takes place, indicating that it consists mainly of O 2p and of small amount of Co 3d component. Since E-F is located near the high-energy edge of this narrow band, the density of states at E-F is finite but negligibly small at room temperature. An energy-gap across E-F opens below 50 K with decreasing temperature. This development of the energy-gap causes the insulating behavior; divergence both in electrical resistivity and Hall coefficient. We calculated thermoelectric power S(T) using the photoemission spectra near E-F. The calculated S(T) shows almost half of the measured value. Large thermoelectric power up to 200 muV/K observed for the Ca3CO4O9 is closely related to the metallic electron transport in a less dispersive band with EF near its band-edge. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.elspec.2004.02.013

Hole-concentration dependence of band structure in (Bi,Pb)(2)(Sr,La)(2)CUO6+delta determined by the angle-resolved photoemission spectroscopy Reviewed

T Kondo, T Takeuchi, T Yokoya, S Tsuda, S Shin, U Mizutani

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 137 663 - 668 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Energy-momentum (E-k) dispersion and the shape of the Fermi surface (FS) in the (Bi,Pb)(2)(Sr,La)(2)CuO6+delta (Bi2201) superconductors of various hole-concentrations were investigated by the angle-resolved photoemission spectroscopy (ARPES) with high energy and momentum resolutions (DeltaE = 10 meV and Deltak = 0.005 Angstrom(-1)). The E-k dispersion is kept rigid and the chemical potential moves towards lower or higher energies with increasing or decreasing hole-concentration, respectively, over a wide hole-concentration range from the nearly optimal-doped condition with a transition temperature of 32 K to a heavily over-doped condition where the superconducting transition disappears. By comparing the shape of the FS determined for the present Bi2201 with that reported for the Bi2Sr2CaCu2O8+delta (Bi2212), we found that the area surrounded by the FS in the Bi2201 is fairly larger than that in the Bi2212. Estimated hole-concentration in the Bi2201 was found to vary from 0.25 to 0.43 holes/Cu, that is more than twice as large as that in the optimally doped La(2-)xSrCuO(4) (LSCO) and Bi2212 superconductors of 0.17 holes/Cu. (C)2004 Elsevier B.V. All fights reserved.

DOI： 10.1016/j.elspec.2004.02.104

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