Faculty Profiles - KONTANI, Hiroshi

Papers - KONTANI, Hiroshi

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

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.

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

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

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

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.

Intrinsic spin and orbital Hall effects in heavy-fermion systems

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

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

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.

Tuning the Dimensionality of the Heavy Fermion Compound CeIn3

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.

Structure of neutron-scattering peaks in both s(++)-wave and s(+/-)-wave states of an iron pnictide superconductor

Onari Seiichiro, Kontani Hiroshi, Sato Masatoshi

PHYSICAL REVIEW B Vol. 81 ( 6 ) 2010.2

Origin of the anomalous Hall effect in the overdoped n-type superconductor Pr(2-x)Ce(x)Cuo(4): Current-vertex corrections due to antiferromagnetic fluctuations

Jenkins G. S., Schmadel D. C., Bach P. L., Greene R. L., Bechamp-Laganiere X., Roberge G., Fournier P., Kontani Hiroshi, Drew H. D.

PHYSICAL REVIEW B Vol. 81 ( 2 ) 2010.1

Violation of Anderson's Theorem for the Sign-Reversing s-Wave State of Iron-Pnictide Superconductors

Onari Seiichiro, Kontani Hiroshi

PHYSICAL REVIEW LETTERS Vol. 103 ( 17 ) 2009.10

*Violation of Anderson's Theorem for the Sign-Reversing s-Wave State of Iron-Pnictide Superconductors Invited Reviewed

Seiichiro Onari and Hiroshi Kontani

Physical Review Letters Vol. 103 page： 177001 2009.10

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

Based on the five-orbital model, we study the effect of local impurity in iron pnictides, and find that the interband impurity scattering is promoted by the d-orbital degree of freedom. This fact means that the fully gapped sign-reversing s-wave state, which is predicted by spin fluctuation theories, is very fragile against impurities. In the BCS theory, only 1% impurities with intermediate strength induce huge pair breaking, resulting in the large in-gap state and prominent reduction in Tc, contrary to the prediction based on simple orbital-less models. The present study provides a stringent constraint on the pairing symmetry and the electronic states in iron pnictides.

Anomalous Hall effect in the t2g orbital kagome lattice due to noncollinearity: Significance of the orbital Aharonov-Bohm effect Reviewed

Takeshi Tomizawa and Hiroshi Kontani

Physical Review B Vol. 80 page： 100401 2009.9

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

A mechanism of spin structure-driven anomalous Hall effect (AHE) in tilted ferromagnetic metals is proposed by taking account of the d-orbital degree of freedom. We find that a conduction electron acquires a Berry phase due to the complex d-orbital wave function, in the presence of noncollinear spin structure and the spin-orbit interaction. The AHE driven by this orbital-derived Berry phase is much larger than the AHE induced by spin chirality, and it naturally explains the salient features of spin structure-driven AHE in pyrochlore Nd2Mo2O7. Since the proposed AHE can occur even for coplanar spin orders (Mz=0), it is expected to emerge in other interesting geometrically frustrated systems.

Anomalous Hall effect in the t2g orbital kagome lattice due to noncollinearity: Significance of the orbital Aharonov-Bohm effect

Tomizawa Takeshi, Kontani Hiroshi

PHYSICAL REVIEW B Vol. 80 ( 10 ) 2009.9

Anomalous and spin Hall effects in magnetic granular films

Inoue Jun-ichiro, Tanaka Takuro, Kontani Hiroshi

PHYSICAL REVIEW B Vol. 80 ( 2 ) 2009.7

Impurity-induced in-gap state and T-c in sign-reversing s-wave superconductors: analysis of iron oxypnictide superconductors

Senga Yuko, Kontani Hiroshi

NEW JOURNAL OF PHYSICS Vol. 11 2009.3

Unconventional Pairing Originating from the Disconnected Fermi Surfaces of Superconducting LaFeAsO1-xFx (vol 101, 087004, 2008)

Kuroki Kazuhiko, Onari Seiichiro, Arita Ryotaro, Usui Hidetomo, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

PHYSICAL REVIEW LETTERS Vol. 102 ( 10 ) 2009.3

Unconventional pairing originating from disconnected Fermi surfaces in the iron-based superconductor

Kuroki Kazuhiko, Onari Seiichiro, Arita Ryotaro, Usui Hidetomo, Tanaka Yukio, Kontani Hiroshi, Aoki Hideo

NEW JOURNAL OF PHYSICS Vol. 11 2009.2

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