Faculty Profiles - KONTANI, Hiroshi

Papers - KONTANI, Hiroshi

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*Universality in Heavy Fermion Systems with General Degeneracy Reviewed

N. Tsujii, H. Kontani, and K. Yoshimura

Physical Review Letter Vol. 94 ( 11 ) page： 057201(4p) 2005.2

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

We discuss the relation between the T2 coefficient of electrical resistivity A and the T-linear specific-heat coefficient γ for heavy-fermion systems with general N, where N is the degeneracy of quasiparticles. A set of experimental data reveals that the Kadowaki-Woods relation, A/γ2=1×10-5  μΩ cm(K mol/mJ)2, collapses remarkably for large-N systems, although this relation has been regarded to be commonly applicable to the Fermi liquids. Instead, based on the Fermi-liquid theory we propose a new relation, A˜/γ˜2=1×10-5 with A˜=A/1/2N(N-1) and γ˜=γ/1/2N(N-1). This new relation exhibits an excellent agreement with the data for the whole range of degenerate heavy fermions.

From Kondo Effect to Fermi Liquid Invited Reviewed

Hiroshi Kontani and Kosaku Yamada

Journal of the Physical Society of Japan Vol. 74 ( 1 ) page： 155-166 2005.1

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

The Kondo effect has been playing an important role in strongly correlated electon systems. The important point is that the magnetic impurity in metals is a typical example of the Fermi liquid. In the system the local spin is conserved in the ground state and continuity with respect to Coulomb repulsion U is satisfied. This nature is satisfied also in the periodic systems as far as the systems remain as the Fermi liquid. This property of the Fermi liquid is essential to understand the cuprate high-Tc superconductors (HTSC). On the basis of the Fermi liquid theory we develop the transport theory such as the resistivity and the Hall coefficient in strongly correlated electron systems, such as HTSC, organic metals and heavy Fermion systems. The significant role of the vertex corrections for total charge- and heat-currents on the transport phenomena is explained. By taking the effect of the current vertex corrections into account, various typical non-Fermi-liquid-like transport phenomena in systems with strong magnetic and/or superconducting flucutations are explained within the Fermi liquid theory.

Magnetic-Field-induced Antiferromagnetism in Two-dimensional Hubbard Model: Analysis of CeRhIn5 Reviewed

Keitaro Sakurazawa, Hiroshi Kontani and Tetsuro Saso

Journal of the Physical Society of Japan Vol. 74 ( 1 ) page： 271-274 2005.1

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

We propose a mechanism for the magnetic-field-induced antiferromagnetic (AF) state in a two-dimensional Hubbard model in the vicinity of the AF quantum critical point (QCP), using the fluctuation-exchange (FLEX) approximation by taking the Zeeman energy due to the magnetic field B into account. In the vicinity of the QCP, we find that the AF correlation perpendicular to B is enhanced, whereas that parallel to B is reduced. This fact means that the finite magnetic field increases TN, with the AF order perpendicular to B. The increment of TN can be understood in terms of the reduction of both quantum and thermal fluctuations due to the magnetic field, which is caused by the self-energy effect within the FLEX approximation. The present study naturally explains the increment of TN in CeRhIn5 under the magnetic field found recently. We will also discuss a relation to some organic metals.

From Kondo effect to Fermi liquid

Kontani H, Yamada K

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 74 ( 1 ) page： 155 - 166 2005.1

Magnetic-field-induced antiferromagnetism in two-dimensional Hubbard model: Analysis of CeRhIn5

Sakurazawa K, Kontani H, Saso T

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 74 ( 1 ) page： 271 - 274 2005.1

Generalized Kadowaki-Woods relation in Er- and Sm-based Heavy Fermion Systems, Invited Reviewed

Hiroshi Kontani

Physica B. Vol. 359-361 page： 202-204 2005

Theory of anisotropic s-wave superconductivity with point-node-like gap minima: Analysis of (Y,Lu)Ni2B2C Reviewed

H. Kontani

Physical Review B Vol. 70 ( 5 ) page： 054507(13p) 2004.8

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

Recent intensive experimental studies revealed that (Y,Lu)Ni2B2C is an extremely anisotropic s-wave superconductor. In addition, its gap function possesses deep point minima, whose ratio of the gap anisotropy is more than 10. On the theoretical side, however, it is nontrivial to understand the origin of such a peculiar superconductivity. In the present paper, we propose a mechanism of the s-wave superconductivity with deep gap minima, based on the theoretical model where strong electron-phonon coupling as well as the moderate magnetic fluctuations coexist. By analyzing the strong coupling Eliashberg equation, we find that s-wave superconducting gap function owing to the electron-phonon coupling becomes highly anisotropic as the magnetic fluctuations increase. The set of model parameters for realizing the strong gap anisotropy in the present model will be appropriate for (Y,Lu)Ni2B2C. According to the present mechanism, (groups of) pairs of gap minima appear at points on the Fermi surface which are connected by the nesting vector Q, in both cases of s-wave superconductors and non-s-wave ones. We briefly discuss other superconductors with highly anisotropic gap function, e.g., PrOs4Sb12 and Na0.33CoO2.

Theory of anisotropic s-wave superconductivity with point-node-like gap minima: Analysis of (Y,Lu)Ni2B2C

Kontani H

PHYSICAL REVIEW B Vol. 70 ( 5 ) 2004.8

Generalized Kadowaki-Woods Relation in Heavy Fermion Systems with Orbital Degeneracy Reviewed

Hiroshi Kontani

Journal of Physical Society of Japan Vol. 73 ( 3 ) 2004.3

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We present a theoretical study of the Kadowaki-Woods relation in the orbitally degenerate periodic Anderson model. Based on the Fermi liquid theory, we derive the generalized Kadowaki-Woods relationin the strong coupling limit, Aγ-2 \approx 10-5 /½ N(N-1) [µΩ cm (mol·K/mJ)2], where A is the coefficient of the T2 term in the resistivity, γ is the T-linear specific heat coefficient, and N is the f-orbital degeneracy. This result naturally explains the remarkably smaller value of Aγ-2 in various orbitally degenerate (mainly Yb-based) heavy Fermion systems, reported by Tsujii et al. [J. Phys.: Condens. Matter 15 (2003) 1993].

Generalized Kadowaki-Woods relation in heavy fermion systems with orbital degeneracy

Kontani H

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 73 ( 3 ) page： 515 - 518 2004.3

Normal-state Hall Angle and Magnetoresistance in Quasi-2D Heavy Fermion CeCoIn5 near a Quantum Critical Point Reviewed

Y. Nakajima, K. Izawa, Y. Matsuda, S. Uji, T. Terashima, H. Shishido, R. Settai, Y. Onuki and H. Kontani

Journal of Physical Society of Japan Vol. 73 ( 1 ) page： 5-8 2004.1

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

The normal-state Hall effect and magnetoresisitance (MR) have been measured in the quasi two dimensional (2D) heavy fermion superconductor CeCoIn5. In the non-Fermi liquid region where the reistivity ρxx exhibits an almost perfect T-linear dependence, the Hall angle varies as cot θH ∝ T2 and MR displays a strong violation of Kohler's rule. We demonstrate a novel relation between the MR and the Hall conductivity, Δ ρxx/ρxx∝ (σxyρxx)2. These results bear a striking resemblance to the normal-state properties of high-Tc cuprates, indicating universal transport properties in the presence of quasi-2D antiferromagnetic fluctuations near a quantum critical point.

Phase Diagram of β'-(BEDT-TTF)2ICl2 under High Pressure Based on the First-Principles Electronic Structure Reviewed

Hiori Kino, Hiroshi Kontani and Tsuyoshi Miyazaki

Journal of Physical Society of Japan Vol. 73 ( 1 ) page： 25-28 2004.1

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

We present a theoretical study on the superconductivity of β'-(BEDT-TTF)2ICl2 at Tc=14.2 K under a high hydrostatic pressure recently found, which is the highest among organic superconductors. In the present work, we study an effective model using the fluctuation-exchange (FLEX) approximation based on the results of first-principles calculation. In the obtained phase diagram, the superconductivity with dxy-like symmetry is realized next to the antiferromagnetic phase, as a result of the one-dimensional to two-dimensional crossover driven by the pressure.

Phase diagram of beta '-(BEDT-TTF)(2)ICl2 under high pressure based on the first-principles electronic structure

Kino H, Kontani H, Miyazaki T

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 73 ( 1 ) page： 25 - 28 2004.1

Normal-state hall angle and magnetoresistance in Quasi-2D heavy fermion CeCoIn5 near a quantum critical point

Nakajima Y, Izawa K, Matsuda Y, Uji S, Terashima T, Shishido H, Settai R, Onuki Y, Kontani H

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 73 ( 1 ) page： 5 - 8 2004.1

高温超伝導体の以上金属相における輸送現象の理論 ─フェルミ液体論に基づく統一的理論─ Invited Reviewed

紺谷浩

日本物理学会誌 Vol. 58 ( 7 ) page： 524-527 2003.7

Origin of superconductivity in beta(')-(BEDT-TTF)(2)ICl2 under high pressure and in beta-(BEDT-TTF)(2)X at atmospheric pressure

Kontani H

PHYSICAL REVIEW B Vol. 67 ( 18 ) 2003.5

Theory of Nernst coefficient in high-T-c cuprates: the role of vertex corrections

Kontani H

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Vol. 388 page： 68 - 69 2003.5

Nernst coefficient in high-T-c superconductors: The role of superconducting fluctuations

Kontani H

ACTA PHYSICA POLONICA B Vol. 34 ( 2 ) page： 799 - 802 2003.2

General formula for the thermoelectric transport phenomena based on Fermi liquid theory: Thermoelectric power, Nernst coefficient, and thermal conductivity

Kontani H

PHYSICAL REVIEW B Vol. 67 ( 1 ) 2003.1

Nernst coefficient and magnetoresistance in high-T-c superconductors: The role of superconducting fluctuations

Kontani H

PHYSICAL REVIEW LETTERS Vol. 89 ( 23 ) 2002.12

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Papers - KONTANI, Hiroshi