Phase transition to the Fulde–Ferrell–Larkin–Ovchinnikov state in a quasi-one-dimensional organic superconductor with anion order

A theoretical study is presented on the effect of anion order on the phase transition from the normal state to a Fulde–Ferrell–Larkin –Ovchinnikov superconducting state in a quasi-one-dimensional organic superconductor (TMTSF)₂ClO₄. The temperature dependence of the upper critical field H_c2(T) is examined. In the absence of anion order, the H_c2(T) curve exhibits a one- to two-dimensional crossover with decreasing temperature T. For a sufficiently large anion order parameter, the dimensional crossover disappears and then a kink appears in the H_c2(T) curve. (paper)