Faculty Profiles - KONTANI, Hiroshi

Papers - KONTANI, Hiroshi

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Comment on "Orbital Order, Structural Transition and Superconductivity in Iron Pnictides" [J. Phys. Soc. Jpn. 79 (2010) 123707] Open Access

Kontani Hiroshi, Onari Seiichiro

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN Vol. 80 ( 5 ) 2011.5

Emergence of fully gapped s(++)-wave and nodal d-wave states mediated by orbital and spin fluctuations in a ten-orbital model of KFe2Se2 Open Access

Saito Tetsuro, Onari Seiichiro, Kontani Hiroshi

PHYSICAL REVIEW B Vol. 83 ( 14 ) 2011.4

Emergence of Fully-Gapped s++-wave and Nodal d-wave States Mediated by Orbital- and Spin-Fluctuations in Ten-Orbital Model for KFe2Se2 Reviewed

T. Saito, S. Onari, and H. Kontani

Phys. Rev. B Vol. 83 page： 140512 2011

Extremely strong-coupling superconductivity in artificial two-dimensional Kondo lattices Reviewed Open Access

Y. Mizukami, H. Shishido, T. Shibauchi, M. Shimozawa, S. Yasumoto, D. Watanabe, M.Yamashita, H. Ikeda, T. Terashima, H. Kontani, and Y. Matsuda

Nature Physics Vol. 7 page： 849 2011

Neutron inelastic scattering peak by dissipationless mechanism in the s++-wave state in iron-based superconductors Reviewed Open Access

S. Onari and H. Kontani

Phys. Rev. B Vol. 84 page： 144518 2011

Linear decrease of critical temperature with increasing Zn substitution in the iron-based superconductor Reviewed

Jun Li, Y. Guo, S. Zhang, S. Yu, Y. Tsujimoto, H. Kontani, K. Yamaura, and E. Takayama-Muromachi

Phys. Rev. B Vol. 84 page： 020513 2011

Origin of Orthorhombic Transition, Magnetic Transition, and Shear Modulus Softening in Iron Pnictide Superconductors: Analysis based on the Orbital Fluctuation Theory Reviewed

H. Kontani, T. Saito, and S. Onari

Phys. Rev. B Vol. 84 page： 024528 2011

Indication of intrinsic spin Hall effect in 4d and 5d transition metals Reviewed Open Access

M. Morota, Y. Niimi, K. Ohnishi, T. Tanaka, H. Kontani, T. Kimura, Y. Otani

Phys. Rev. B Vol. 83 page： 174405 2011

Nonmagnetic impurity effects and neutron scattering spectrum in iron pnictides

Onari S., Kontani H.

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS Vol. 470 ( 20 ) page： 1007-1009 2010.11

Orbital fluctuation theory in iron pnictides: Effects of As-Fe-As bond angle, isotope substitution, and Z(2)-orbital pocket on superconductivity Open Access

Saito Tetsuro, Onari Seiichiro, Kontani Hiroshi

PHYSICAL REVIEW B Vol. 82 ( 14 ) 2010.10

Orbital fluctuation theory in iron pnictides: Effects of As-Fe-As bond angle, isotope substitution, and Z2-orbital pocket on superconductivity Reviewed Open Access

Tetsuro Saito, Seiichiro Onari, Hiroshi Kontani

Physical Review B Vol. 82 ( 14 ) page： 144510 2010.10

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

We study the pairing mechanism in iron pnictide superconductors based on the five-orbital Hubbard-Holstein model. Due to Fe-ion oscillations, the s-wave superconducting (SC) state without sign reversal (s++-wave state) is induced by orbital fluctuations by using realistic model parameters. The virtue of the present theory is that the famous empirical relation between Tc and the As-Fe-As bond angle is automatically explained since the electron-phonon coupling that creates the orbital fluctuations is the strongest when the As4 tetrahedron is regular. The negative iron isotope effect is also reproduced. In addition, the magnitude of the SC gap on hole pockets is predicted to be rather insensitive to the corresponding d orbital (xz/yz or z2 orbital), which is consistent with the recent bulk-sensitive angle-resolved photoemission spectroscopy (ARPES) measurement for (Ba,K)Fe2As2 and BaFe2(As,P)2. These obtained results indicate that the orbital fluctuation mediated s++-wave state is a plausible candidate for iron pnictides.

DOI： 10.1103/PhysRevB.82.144510

Terahertz Hall measurements on optimally doped single-crystal Bi2Sr2CaCu2O8+x Open Access

Jenkins G. S., Schmadel D. C., Sushkov A. B., Gu G. D., Kontani H., Drew H. D.

PHYSICAL REVIEW B Vol. 82 ( 9 ) 2010.9

Anomalous Hall effect due to noncollinearity in pyrochlore compounds: Role of orbital Aharonov-Bohm effect Open Access

Tomizawa Takeshi, Kontani Hirhoshi

PHYSICAL REVIEW B Vol. 82 ( 10 ) 2010.9

Anomalous Hall effect due to noncollinearity in pyrochlore compounds: Role of orbital Aharonov-Bohm effect Reviewed Open Access

Takeshi Tomizawa, Hirhoshi Kontani

physical Review B Vol. 82 ( 10 ) page： 104412 2010.9

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

To elucidate the origin of spin structure-driven anomalous Hall effect (AHE) in pyrochlore compounds, we construct the t2g-orbital kagome lattice model and analyze the anomalous Hall conductivity (AHC). We reveal that a conduction electron acquires a Berry phase due to the complex d-orbital wave function in the presence of spin-orbit interaction. This orbital Aharonov-Bohm (AB) effect produces the AHC that is drastically changed in the presence of noncollinear spin structure. In both ferromagnetic compound Nd2Mo2O7 and paramagnetic compound Pr2Ir2O7, the AHC given by the orbital AB effect totally dominates the spin-chirality mechanism and succeeds in explaining the experimental relation between the spin structure and the AHC.

DOI： 10.1103/PhysRevB.82.104412

Intrinsic spin and orbital Hall effects in heavy-fermion systems Open Access

Tanaka T., Kontani H.

PHYSICAL REVIEW B Vol. 81 ( 22 ) 2010.6

Tight-binding study of anomalous Hall effect in ferromagnetic 3d transition metals

Naito T., Hirashima D. S., Kontani H.

PHYSICAL REVIEW B Vol. 81 ( 19 ) 2010.5

Orbital-Fluctuation-Mediated Superconductivity in Iron Pnictides: Analysis of the Five-Orbital Hubbard-Holstein Model Open Access

Kontani Hiroshi, Onari Seiichiro

PHYSICAL REVIEW LETTERS Vol. 104 ( 15 ) 2010.4

Orbital-Fluctuation-Mediated Superconductivity in Iron Pnictides: Analysis of the Five-Orbital Hubbard-Holstein Model Reviewed Open Access

Hiroshi Kontani, Seiichiro Onari

Physical Review Letters Vol. 104 ( 15 ) page： 157001 2010.4

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

In iron pnictides, we find that the moderate electron-phonon interaction due to the Fe-ion oscillation can induce the critical d-orbital fluctuations, without being prohibited by the Coulomb interaction. These fluctuations give rise to the strong pairing interaction for the s-wave superconducting (SC) state without sign reversal (s++-wave state), which is consistent with experimentally observed robustness of superconductivity against impurities. When the magnetic fluctuations due to Coulomb interaction are also strong, the SC state shows a smooth crossover from the s-wave state with sign reversal (s±-wave state) to the s++-wave state as impurity concentration increases.

DOI： 10.1103/PhysRevLett.104.157001

Tuning the Dimensionality of the Heavy Fermion Compound CeIn3 Open Access

Shishido H., Shibauchi T., Yasu K., Kato T., Kontani H., Terashima T., Matsuda Y.

SCIENCE Vol. 327 ( 5968 ) page： 980-983 2010.2

Structure of Neutron-Scattering Peak in both s++ wave and s+- wave states of an Iron pnictide Superconductor Reviewed

Seiichiro Onari, Hiroshi Kontani, Masatoshi Sato

physical Review B Vol. 81 ( 6 ) page： 060504(R) 2010.2

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

We study the neutron-scattering spectrum in iron pnictides based on the random-phase approximation in the five-orbital model for fully gapped s-wave states with sign reversal (s±) and without sign reversal (s++). In the s++-wave state, we find that a prominent hump structure appears just above the spectral gap by taking account of the quasiparticle damping γ due to strong electron-electron correlation: as the superconductivity develops, the reduction in γ gives rise to the large overshoot in the spectrum above the gap. The obtained hump structure looks similar to the resonance peak in the s±-wave state, although the height and weight of the peak in the latter state is much larger. In the present study, experimentally observed broad spectral peak in iron pnictides is naturally reproduced by assuming the s++-wave state.

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Papers - KONTANI, Hiroshi