Fluctuation exchange theory for superconductivity of -electron systems with multipole degrees of freedom

Kubo, Katsunori ; Hotta, Takashi

Recently, an interesting possibility of superconductivityinduced by multipole fluctuations has been discussed insome -electron materials. In order to clarify such exotic superconductivity from a microscopic viewpoint, we apply fluctuation exchange approximationto an -electron model with active orbital degree of freedomon the basis of a - coupling scheme. First, we evaluate orbital dependent fluctuations andeffective paring interactions within the FLEX approximation. Then, we determine the symmetry of the gap function amongpossible superconducting states by solving the Eliashberg equation. In particular, we pay our attention to the effect of crystallineelectric field on the appearance of superconductivity. By further decomposing complex orbital dependent fluctuationsinto multipole components, we also discuss possible relevance ofmultipole fluctuations to exotic superconductivity.