Peculiar Critical Field Behaviour in the Recectly Discovered Ambient Pressure Organic Superconductor (BEDT-TTF)2Cu (NCS)2(Tc=10.4K)

An upper critical field measurement in the recently discovered ambient pressure organic superconductor (BEDT-TTF) 2 Cu(NCS) 2 ( T c =10.4K) is reported. Three- to two-dimensional crossover behaviour is observed in the temperature dependence of the parallel critical field. The anisotropy of the coherence length near T c , ξ c /ξ a * , is about 19 and ξ a * (0) is smaller than the lattice spacing along the a * -axis. An unusual temperature dependence of the perpendicular critical field is observed far below T c . It is confirmed that deuterated salt is also an ambient pressure superconductor with a slightly higher T c (11 K).