Fulde-Ferrell-Larkin-Ovchinnikov State in a Quasi-Two-Dimensional Organic Superconductor

Abstract

The possibility of the existence Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in quasi-low-dimensional organic superconductors is discussed. The critical field and the wave number q of the spatial oscillation are calculated on the basis of a tight binding model of κ-[BEDT-TTF]_{2I₃}, as an example. The critical fields H_c at T=0 are estimated to be roughly 1.5, 2, and 2.5 times the Pauli paramagnetic limit H_P for s-wave, d_xy-wave, and d_x²_-y²-wave FFLO states, respectively. We discuss which properties of the structure of the Fermi surface enhance the critical field and are relevant to the direction of q. We show that the number of the lines on the displaced Fermi surfaces due to the Zeeman energy which simaltaneously touch by translation p → p+q are important in addition to the curvature of the Fermi surface and the density of states.