Pressure dependence of the transport properties of the molecular superconductor, κ-(BEDT TTF)₂Cu(NCS)₂

Abstract

The molecular superconductor kappa -(BEDT TTF)2Cu(NCS)2, which has a superconducting transmission temperature, Tc, as high as 10.5 K, exhibits a very high resistivity at ambient pressure ( approximately=10-1 Omega cm at room temperature) which rises on cooling to reach a maximum near 90 K. The authors find that with the application of pressures of up to 2.5 kbar this peak remains strong and is progressively sharpened, but that above 2.5 kbar the size of the resistive peak falls very quickly. In their crystals the resistively measured Tc is 7 K at ambient pressure and remains constant up to 3 kbar, before falling steeply at 1.8 K kbar-1 above this pressure. The authors attribute the unusual temperature dependence of the normal state conductivity to a structural phase transition which at pressures below about 3 kbar couples to the conduction electrons. They discuss whether or not the superconducting properties are affected by the proximity of the material to the phase transition.