第35回 原研・兵県大合同コロキウム

日時: 平成20年1月17日(木) 16:00〜
Date and time: 17th Jan. (Thu.) 16:00〜
場所: SPring-8, 萌光館
Place: SPring-8, "HOUKOUKAN" seminar room
Title: Superconducting states in two-orbital systems
講演者: 久保勝規 氏 (原子力機構・先端科学研究センター)
Speaker: Dr. Katsunori Kubo (Advanced Science Research Center, JAEA)
Abstract:

We discuss possible superconducting states in systems with orbital degree of freedom. In a multi-orbital system, exotic pairing states such as even-parity spin-triplet [1-3] and odd-parity spin-singlet states are possible.These states are prohibited by the Pauli principle in a single-orbital system, but allowed in a multi-orbital system by constructing a pair with antisymmetrical orbitals. To discuss possibility of such states, we first consider a two-orbital Hubbard model with the same Fermi surface for both orbitals on a square lattice.Then, we apply fluctuation exchange (FLEX) approximation and indeed find that such exotic states realize in the two-orbital Hubbard model [4].We also consider an eg orbital model on a square lattice and apply FLEX approximation. In the eg orbital model, the number of Fermi surfaces and their structures depend on the ratio of the Slater-Koster integrals. Then, we find several superconducting states depending on the structure of the Fermi surfaces and the number of electrons per site. In particular, we find that pairing states with a finite total momentum like the Fulde-Ferrell-Larkin-Ovchinnikov state appear even without a magnetic field. When two Fermi surfaces have structures similar to each other, an exotic pair with a finite total momentum, which connects the centers of the Fermi surfaces, can be stabilized.