Interplane penetration depth and coherent transport in organic superconductors

Abstract

Measurements of the interlayer penetration depth {lambda}{sub {perpendicular}} have been performed on single crystals of the organic superconductors {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br and {kappa}-(ET){sub 2}Cu(NCS){sub 2}. We find that {lambda}{sub {perpendicular}}(0){approx}130 {micro}m for both materials. The normalized superfluid density {rho}{sub {perpendicular}} = [{lambda}{sub {perpendicular}}(0)/{lambda}{sub {perpendicular}} (T)]{sup 2} may be fit equally well to a power law 1{rho}{sub {perpendicular}} {approx} T{sup n} with n = 1.3-1.5 or to the form 1{rho}{sub {perpendicular}} = {alpha}(t{sup 2}/T{sub c})/(T+T*), consistent with a d-wave pairing state with impurity scattering. The data imply coherent transport between conducting planes, in agreement with recent magnetoresistive measurements [J. Singleton, P. A. Goddard, A. Ardavan, N. Harrison, S. J. Blundell, J. A. Schlueter, and A. M. Kini, Phys. Rev. Lett. 88, 037001 (2002)] and in contrast to the copper oxides.