Magnetic field and temperature phase diagram of the pressurized organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br in the field parallel to the conducting plane

The upper critical field H c 2 of the layered organic superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br has been studied with emphasis on the field direction parallel to the conducting plane. Application of hydrostatic pressure changes the shape of the H c 2 (T) diagram, removing a notable curvature observed at ambient pressure in the high-temperature region and giving almost linear dependence. The change is ascribed to the dominance of the orbital pair-breaking effect under pressure as opposed to the Pauli paramagnetic limiting of H c 2 at ambient pressure. An abrupt change by pressure of the slope of the H c 2 (T) curve in a temperature range near T c is ascribed to the phase change in the material due to the ordering of the ethylene fragments of the BEDT-TTF molecules.