Reentrant meissner effect in the organic superconductor κ-ET2Cu[N(CN)2]Cl1−xBrx under pressure

Metallic conductivity and superconductivity (SC) in the title compound is only observed under hydrostatic pressure. The critical pressure for the occurrence of SC (Pcrit = 290 bar for x=0) is lowered with increasing Br-content. In a pressure range above this pressure, whose width seems to depend on sample quality, reentrant SC is observed, presumably due to a competition with a magnetic ground state. We show by means of DC diamagnetic measurements, that the reentrant SC is a volume property and that the reentrant transition is a first order transition from a SC to a magnetically ordered state.