Interplane penetration depth and coherent transport in organic superconductors

Measurements of the interlayer penetration depth lambda(perpendicular to) have been performed on single crystals of the organic superconductors kappa-(ET)(2)Cu[N(CN)(2)]Br and kappa-(ET)(2)Cu(NCS)(2). We find that lambda(perpendicular to)(0)approximate to 130 mu m for both materials. The normalized superfluid density rho(perpendicular to)=[lambda(perpendicular to)(0)/lambda(perpendicular to)(T)](2) may be fit equally well to a power law 1-rho(perpendicular to)similar to T-n with n=1.3-1.5 or to the form 1-rho(perpendicular to)=alpha(T-2/T-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.