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Robustness of s-wave superconductivity against Coulomb interactions in NaxCoO2

Yada Keiji, Kontani Hiroshi

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460 巻頁： 483-484 2007年9月

Theory of thermal conductivity in high-T-c superconductors below T-c: Comparison between hole- and electron-doped systems

Hara Hideyuki, Kontani Hiroshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 巻 ( 7 ) 2007年7月

Theory of Thermal Conductivity in High-Tc Superconductors below Tc: Comparison between Hole- and Electron-Doped Systems 査読有り

Hideyuki Hara, Hiroshi Kontan

Journal of the Physical Society of Japan 76 巻 ( 18 ) 頁： 184416 2007年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

In hole-doped high-Tc superconductors, thermal conductivity κ increases drastically just below Tc, which has been considered as a hallmark of a nodal gap. In contrast, such a coherence peak in κ is not visible in electron-doped compounds, which may indicate a full-gap state such as a d+is-wave state. To settle this problem, we study κ in the Hubbard model using the fluctuation-exchange (FLEX) approximation, which predicts that the nodal d-wave state is realized in both hole- and electron-doped compounds. The contrasting behavior of κ in both compounds originates from the differences in the hot/cold spot structure. In general, a prominent coherence peak in κ appears in line-node superconductors only when the cold spot exists on the nodal line.

Theory of Infrared Hall Conductivity Based on the Fermi Liquid Theory: Analysis of High-Tc Superconductors 査読有り

76 巻頁： 074707 2007年7月

Theory of Thermal Conductivity in High-Tc Superconductors below Tc: Comparison between Hole- and Electron-Doped Systems 査読有り

Hideyuki Hara, and Hiroshi Kontani

Journal of the Physical Society of Japan 76 巻頁： 073705 2007年7月

Theory of Infrared Hall Conductivity Based on the Fermi Liquid Theory: Analysis of High-Tc Superconductors 査読有り

H. Kontani

Journal of the Physical Society of Japan 76 巻 ( 07 ) 頁： 074707 2007年7月

記述言語：英語掲載種別：研究論文（学術雑誌）

We study optical Hall conductivity for high-Tc superconductors on the basis of microscopic Fermi liquid theory. Current vertex corrections (CVCs) are correctly taken into account to satisfy the conservation laws, and are performed for the first time for optical conductivities based on the fluctuation-exchange (FLEX) approximation. We find that (I) the CVC emphasizes the ω-dependence of σxy(ω) significantly when the antiferromagnetic (AF) fluctuations are strong. For this reason, the relation σxy(ω)∼{σxx(ω)}2, which is satisfied in the extended Drude model given by the relaxation time approximation (RTA), is completely violated for a wide range of frequencies. Consequently, (II) the optical Hall coefficient RH(ω) strongly depends on ω below infrared frequencies, which is consistent with experimental observations. Interestingly, although σxx(ω) does not follow a simple Drude form due to the ω-dependence of the relaxation time τ, θH(ω) and σxy(ω) follow approximate simple Drude forms since the ω-dependences of τ and CVC almost cancel each other out. In conclusion, anomalous optical transport phenomena in high-Tc superconductors, which had been frequently assumed to be as evidence of the breakdown of the Fermi liquid state, can be well explained in terms of the nearly AF Fermi liquid once the CVC is taken into account.

Theory of infrared hall conductivity based on the fermi liquid theory: Analysis of high-T-c superconductors

Kontani Hiroshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 巻 ( 7 ) 2007年7月

Intrinsic anomalous Hall effect in ferromagnetic metals studied by the multi-d-orbital tight-binding model

Kontani Hiroshi, Tanaka Takuro, Yamada Kosaku

PHYSICAL REVIEW B 75 巻 ( 18 ) 2007年5月

Infrared Hall conductivity in optimally doped Bi2Sr2CaCu2O8+δ : Drude behavior examined by experiment and fluctuation-exchange-model calculations 査読有り

D.C. Schmadel, G. S. Jenkins, J.J. Tu, G.D. Gu, H. Kontani, and H. D. Drew

Physical Review B 75 巻 ( 14 ) 頁： 140506R (4p) 2007年4月

記述言語：英語掲載種別：研究論文（学術雑誌）

The temperature dependence of the Hall conductivity is reported at mid- and far-IR frequencies for cleaved single crystals. A nearly simple Drude behavior is observed with a scattering rate that is linear in temperature and nearly frequency independent. The Hall data are in good agreement with calculations based on the fluctuation-exchange interaction when current vertex corrections are included. The σxy quasiparticle spectral weight is suppressed to 0.09 times the band value, compared with 0.33 times the band value for σxx.

Infrared Hall conductivity in optimally doped Bi2Sr2CaCu2O8+delta: Drude behavior examined by experiment and fluctuation-exchange-model calculations

Schmadel D. C., Jenkins G. S., Tu J. J., Gu G. D., Kontani Hiroshi, Drew H. D.

PHYSICAL REVIEW B 75 巻 ( 14 ) 2007年4月

Hall effect in the quasi two-dimensional strongly correlated metal CeMIn5 (M = Co, Rh)

Nakajima Y., Shishido H., Nakai H., Shibauchi T., Izawa K., Behnia K., Hedo H., Uwatoko Y., Matsumoto T., Settai R., Onuki Y., Kontani H., Matsuda Y.

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 334 - 336 2007年3月

Anomalous transport phenomena in CeCoIn5 close to quantum critical point

Onari S., Kontani H., Tanaka Y.

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 359-361 2007年3月

Renormalization of Coulomb interactions in s-wave superconductor NaxCoO2

Yada Keiji, Kontani Hiroshi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 684 - 686 2007年3月

Nonlocal effect of local nonmagnetic impurity in high-T-c superconductors: Induced local moment and huge residual resistivity

Kontani Hiroshi, Ohno Masanori

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 巻 ( 2 ) 頁： 483-485 2007年3月

Non-fermi liquid behavior in the magnetotransport of CeMln(5) (M : Co and Rh): Striking similarity between quasi two-dimensional heavy fermion and high-T-c cuprates

Nakajima Y., Shishido H., Nakai H., Shibauchi T., Behnia K., Izawa K., Hedo M., Uwatoko Y., Matsumoto T., Settai R., Onuki Y., Kontani H., Matsuda Y.

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 巻 ( 2 ) 2007年2月

Non-Fermi Liquid Behavior in the Magnetotransport of CeMIn5 (M: Co and Rh): Striking Similarity between Quasi Two-Dimensional Heavy Fermion and High-Tc Cuprates 査読有り

Y. Nakajima, H. Shishido, H. Nakai, T. Shibauchi, K. Behnia, K. Izawa, M. Hedo, Y. Uwatoko, T. Matsumoto, R. Settai, Y. Ōnuki, H. Kontani, and Y. Matsuda

Journal of the Physical Society of Japan 76 巻 ( 02 ) 頁： 024703 2007年2月

記述言語：英語掲載種別：研究論文（学術雑誌）

We present a systematic study of the dc-resistivity, Hall effect, and magnetoresistance in the normal state of quasi two-dimensional (2D) heavy fermion superconductors CeMIn5 (M: Rh and Co) under pressure. Here the electronic system evolves with pressure from an antiferromagnetic (AF) metal, through a highly unconventional non-Fermi liquid, and finally into a Fermi-liquid state. The novelty of these materials is best highlighted when compared with LaMIn5, a system with similar electronic structures, which shows a nearly temperature independent Hall coefficient and a magnetoresisitance which is well described by the classical Kohler's rule. In sharp contrast, in CeMIn5, the amplitude of the Hall coefficient increases dramatically with decreasing temperature, reaching at low temperatures a value significantly larger than 1/ne, where n is the carrier number. Furthermore, the magnetoresistance is characterized by T- and H-dependence which clearly violate Kohler's rule. We found that the cotangent of the Hall angle cot ΘH varies as T2, and the magnetoresistance is well scaled by the Hall angle as Δρxx/ρxx∝tan 2ΘH. These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the quantum critical point. We lay particular emphasis on the striking resemblance of these anomalous magnetotransport with those of the high-Tc cuprates. We argue that features commonly observed in quasi 2D heavy fermion and cuprates very likely capture universal features of strongly correlated electron systems in the presence of strong AF fluctuations, holding the promise of bridging our understanding of heavy fermion systems and high-Tc cuprates.

Degeneracy dependence of the Kadowaki-Woods relation in heavy-fermion systems

Tsujii Naohito, Kontani Hiroshi, Yoshimura Kazuyoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 巻頁： 174-177 2007年1月

Intrinsic anomalous Hall effect in ferromagnetic metals studied by the multi- d -orbital tight-binding model 査読有り

Hiroshi Kontani, Takuro Tanaka, and Kosaku Yamada

Physical Review B 75 巻 ( 18 ) 頁： 184416 2007年

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

To elucidate the origin of anomalous Hall effect (AHE) in ferromagnetic transition metals, we study the intrinsic AHE based on a multiorbital (dxz,dyz) tight-binding model. We find that a large anomalous velocity comes from the off-diagonal (interorbital) hopping. For this reason, the present model shows a large intrinsic anomalous Hall conductivity (AHC) which is compatible with typical experimental values in ferromagnets (102–103 Ω−1 cm−1), without the necessity to assume a special band structure at the Fermi level. In good metals where ρ is small, the intrinsic AHC is constant (dissipationless) as found by Karplus and Luttinger. In bad metals, however, we find that the AHC is proportional to ρ−2 when ℏ∕2τ is larger than the minimum band splitting measured from the Fermi level Δ. This crossover behavior of the intrinsic AHE, which was derived in J. Phys. Soc. Jpn. 63, 2627 (1994), was recently observed in various ferromagnetic metals universally by Asamitsu We also stress that the present (dxz,dyz) tight-binding model shows a huge spin Hall effect in a paramagnetic state.

Optical conductivity of bad metals: Shift of the Drude peak

T. Mutou and H. Kontani

Physical Review B 74 巻 ( 11 ) 頁： 115107 (6p) 2006年12月

Theoretical study of the phase diagram of beta '-(BEDT-TTF)(2)AuCl2 at hydrostatic pressure

Kino Hiori, Kontani Hiroshi, Miyazaki Tsuyoshi

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 巻 ( 10 ) 2006年10月

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