Persistence to High Temperatures of Interlayer Coherence in an Organic Superconductor

The interlayer magnetoresistance ρzz of the organic metal κ-(BEDT-TTF)₂Cu(NCS)₂ is studied in fields of up to 45 T and at temperatures T from 0.5 to 30 K. The peak in ρzz seen in in-plane fields, a definitive signature of interlayer coherence, remains to Ts exceeding the Anderson criterion for incoherent transport by a factor ~30. Angle-dependent magnetoresistance oscillations are modeled using an approach based on field-induced quasiparticle paths on a 3D Fermi surface, to yield the T dependence of the scattering rate τ^-1. The results suggest that τ^-1 does not vary strongly over the Fermi surface, and that it has a T² dependence due to electron-electron scattering.