2010年9月21日 10時30分

Recently, the noncentrosymmetric system provides many research topics, like spintronics and parity-mixing superconductivity. The system is relating with the recent topic of topological insulator, in which the wave function at the Dirac point recovering the inversion symmetry plays an important role. The lack of inversion symmetry is introduced by an antisymmetric spin-orbit coupling (ASOC), like Rashba-term, which also breaks the rotational symmetry in the spin space (SU(2)). For superconductivity, even though either the inversion symmetry or the SU(2) symmetry is broken, it is possible to classify into the spin-singlet and spin-triplet superconducting states, because of the antisymmetry of fermion exchange in a Cooper pair. On the other hand, superconductivity in the noncentrosymmetric system is essentially a parity-mixing superconductivity, where the spin-singlet and spin-triplet Cooper pairs coexist. In the talk, a theory of mechanism of parity-mixing superconductivity assisted by Dzyaloshinski-Moriya-type spin fluctuations will be developed.