Hiroshi Kontani

Unconventional pairing originating from the disconnected Fermi surfaces of superconducting LaFeAsO1-xFx.

For a newly discovered iron-based high T_{c} superconductor LaFeAsO1-xFx, we have constructed a minimal model, where inclusion of all five Fe d bands is found to be necessary. The random-phase approximation is applied to the model to investigate the origin of superconductivity. We conclude that the multiple spin-fluctuation modes arising from the nesting across the disconnected Fermi surfaces realize an extended s-wave pairing, while d-wave pairing can also be another candidate.

Orbital-fluctuation-mediated superconductivity in iron pnictides: Analysis of the five-orbital hubbard-holstein model

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.

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

We have investigated spin Hall effects in 4

Intrinsic spin Hall effect and orbital Hall effect in 4 d and 5 d transition metals

d

Hall effect and resistivity in high- T c superconductors: The conserving approximation

and 5

Violation of Anderson's theorem for the sign-reversing s-wave state of iron-pnictide superconductors.

d

Phase Diagram of Superconductivity on the Anisotropic Triangular Lattice Hubbard Model: An Effective Model of κ-(BEDT-TTF) Salts

transition metals, Nb, Ta, Mo, Pd and Pt, by incorporating the spin absorption method in the lateral spin valve structure; where large spin current preferably relaxes into the transition metals, exhibiting strong spin-orbit interactions. Thereby nonlocal spin valve measurements enable us to evaluate their spin Hall conductivities. The sign of the spin Hall conductivity changes systematically depending on the number of

Universality in heavy fermion systems with general degeneracy.

d

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

electrons. This tendency is in good agreement with the recent theoretical calculation based on the intrinsic spin Hall effect.

Plaquette resonating-valence-bond ground state of CaV4O9.

We study the intrinsic spin Hall conductivity (SHC) in various