Systematic investigation of electronic structure in BEDT-TTF based organic superconductors withT c above 10 K; ?-(BEDT-TTF)2 X (X=Cu(NCS)2, Cu[N(CN)2]Br, and Cu(CN)[N(CN)2

Abstract

The electronic structure of the title superconductors has been investigated by electrical resistivity, complex susceptibility, and electron paramagnetic resonance (EPR) measurements. The superconducting properties (pressure dependence ofT c , magnetic penetration depth, upper critical field, and so on) of these three salts are similar to each other, while transport properties in the normal state have shown a large variety in the temperature dependence. In order to clarify the electronic structure in the normal state, the EPR parameters, the spin susceptibility (χ spin), and the linewidth (ΔH pp), are compared. An anomalous temperature dependence of theg-value has been observed below 150 K in the Cu(NCS)2 and Cu(CN)[N(CN)2] salts.