Faculty Profiles - KONTANI, Hiroshi

Papers - KONTANI, Hiroshi

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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 Vol. 75 ( 18 ) 2007.5

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

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

Physical Review B Vol. 75 ( 14 ) page： 140506R (4p) 2007.4

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

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 Vol. 75 ( 14 ) 2007.4

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 Vol. 310 ( 2 ) page： 334 - 336 2007.3

Anomalous transport phenomena in CeCoIn5 close to quantum critical point

Onari S., Kontani H., Tanaka Y.

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 310 ( 2 ) page： 359-361 2007.3

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 Vol. 310 ( 2 ) page： 483-485 2007.3

Renormalization of Coulomb interactions in s-wave superconductor NaxCoO2

Yada Keiji, Kontani Hiroshi

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Vol. 310 ( 2 ) page： 684 - 686 2007.3

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 Vol. 76 ( 2 ) 2007.2

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 Reviewed

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 Vol. 76 ( 02 ) page： 024703 2007.2

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

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 Vol. 76 page： 174-177 2007.1

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

Hiroshi Kontani, Takuro Tanaka, and Kosaku Yamada

Physical Review B Vol. 75 ( 18 ) page： 184416 2007

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

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 Vol. 74 ( 11 ) page： 115107 (6p) 2006.12

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 Vol. 75 ( 10 ) 2006.10

Optical conductivity of bad metals: Shift of the Drude peak

Mutou Tetsuya, Kontani Hiroshi

PHYSICAL REVIEW B Vol. 74 ( 11 ) 2006.9

Effect of a nonmagnetic impurity in a nearly antiferromagnetic Fermi liquid: Magnetic correlations and transport phenomena

Kontani Hiroshi, Ohno Masanori

PHYSICAL REVIEW B Vol. 74 ( 1 ) 2006.7

Transport phenomena in a three-dimensional system close to the magnetic quantum critical point: The conserving approximation with current vertex corrections, Reviewed

S. Onari, H. Kontani, and Y. Tanaka,

Physical Review B Vol. 74 ( 22 ) page： 224434 (10p) 2006.6

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

It is known that various transport coefficients strongly deviate from conventional Fermi-liquid behaviors in many electron systems which are close to antiferromagnetic (AF) quantum critical points (QCP). For example, Hall coefficients and Nernst coefficients in three-dimensional heavy fermion CeCoIn5 and CeCu6–xAux increase strikingly at low temperatures, whose overall behaviors are similar to those in high-Tc cuprates. These temperature dependencies are too strong to explain in terms of the relaxation time approximation. To elucidate the origin of these anomalous transport phenomena in three-dimensional systems, we study the current vertex corrections (CVC) based on the fluctuation exchange approximation, and find out the decisive role of the CVC. The main finding of the present paper is that the Hall coefficient and the Nernst coefficient strongly increase thanks to the CVC in the vicinity of the AF QCP, irrespective of dimensionality. We also study the relaxation time of quasiparticles, and find that "hot points" and "cold lines" are formed in general three-dimensional systems due to strong AF fluctuations.

Effect of a nonmagnetic impurity in a nearly antiferromagnetic Fermi liquid: Magnetic correlations and transport phenomena Reviewed

H. Kontani and M. Ohno

Physical Review B Vol. 74 ( 01 ) page： 014406 (21p) 2006.6

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

In nearly antiferromagnetic (AF) metals such as high-Tc superconductors (HTSCs), a single nonmagnetic impurity frequently causes nontrivial widespread change of the electronic states. To elucidate this long-standing issue, we study a Hubbard model with a strong onsite impurity potential based on an improved fluctuation-exchange (FLEX) approximation, which we call the GVI-FLEX method. This model corresponds to the HTSC with dilute nonmagnetic impurity concentration. We find that (i) both local and staggered susceptibilities are strongly enhanced around the impurity. By this reason, (ii) the quasiparticle lifetime as well as the local density of states are strongly suppressed in a wide area around the impurity (like a Swiss cheese hole), which causes the "huge residual resistivity" beyond the s-wave unitary scattering limit. We stress that the excess quasiparticle damping rate caused by impurities has strong k-dependence due to non-s-wave scatterings induced by many-body effects, so the structure of the "hot spot/cold spot" in the host system persists against impurity doping. This result could be examined by the ARPES measurements. In addition, (iii) only a few percent of impurities can cause a "Kondo-like" upturn of resistivity (d/dT<0) at low T when the system is very close to the AF quantum critical point. The results (i)–(iii) obtained in the present study, which cannot be derived by the simple FLEX approximation, naturally explain the main impurity effects in HTSCs. We also discuss the impurity effect in heavy fermion systems and organic superconductors.

Transport phenomena in a three-dimensional system close to the magnetic quantum critical point: The conserving approximation with current vertex corrections

Onari Seiichiro, Kontani Hiroshi, Tanaka Yukio

PHYSICAL REVIEW B Vol. 73 ( 22 ) 2006.6

Grand Kadowaki-Woods relation of heavy-fermion systems with degeneracy

Tsujii N., Kontani H., Yoshimura K.

PHYSICA B-CONDENSED MATTER Vol. 378-80 page： 730 - 731 2006.5

Electron-Phonon Mechanism for Superconductivity in Na0.35CoO2: Valence-Band Suhl-Kondo Effect Driven by Shear Phonons Reviewed

K. Yada and H. Kontai

Journal of the Physical Society of Japan Vol. 75 ( 3 ) page： 033705 (4p) 2006.3

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

To study the possible mechanism of superconductivity in Na0.35CoO2, we examine the interaction between all the relevant optical phonons (breathing and shear phonons) and t2g (a1g+eg') electrons of Co ions, and study the transition temperature for s-wave superconductivity. The obtained Tc is very low when the eg' valence bands are far below the Fermi level. However, Tc is strongly enhanced when the top of the eg' valence bands is close to the Fermi level (e.g., -50 meV), thanks to the interband hopping of Cooper pairs caused by shear phonons. This “valence-band Suhl–Kondo mechanism" due to shear phonons is important in understanding the superconductivity in Na0.35CoO2. By the same mechanism, the kink structure of the band dispersion observed by angle-resolved photoemission spectroscopy (ARPES) measurements, which indicates the strong mass enhancement (m*/m∼3) due to optical phonons, is also explained.

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