Interplane penetration depth and coherent transport in organic superconductors

Measurements of the interlayer penetration depth λ □ have been performed on single crystals of the organic superconductors κ- (ET) 2 Cu [N (CN) 2] Br and κ- (ET) 2 Cu (NCS) 2. We find that λ □ (0) ≈ μm for both materials. The normalized superfluid density ρ □ = [λ □ (0) / λ □ (T)] 2 may be fit equally well to a power law 1-ρ □□ Tn with n=1.3-1.5 or to the form 1 - ρ□ = α (T2 / TC) / (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 and in contrast to the copper oxides.