Superfluid density and pairing in planar organic superconductors

Abstract

We calculate self-consistently in-plane superfluid density rho(parallel to)(s) in planar organic superconductors to]for three types of pairing symmetry: d(x2-y2), d(xy)-like and extended s-wave pairing. Assuming strong dimerization, we consider a single band model with elliptical Fermi surface to evaluate: the temperature dependence rho(parallel to)(s) (T) in K-(BEDT-TTF)(2)X compounds for those types of pairing. The obtained results, compared with measurements of the superfluid density in k-(BEDT-TTF)(2)Cu[N(CN)(2)]Br, strongly suggest that in these compounds the gap symmetry, influenced by cooling history, in the "ground state" with the least disorder is of the extended s-wave type. Possible physical reasons for agreement of d(x2-y2), and/or isotropic s-wave pairing with experirncntal results in more disordered "interniediate state" are discussed.