Investigations of the transport properties of the organic superconductors β-(BEDT-TTF)2I3 and βt-(BEDT-TTF)2I3

Abstract

The temperature dependence of the resistivity, thermopower and ac-susceptibility of the organic superconductors β-(BEDT-TTF )2I3 and βt-(BEDT-TTF)2I3 were investigated. A metal-metal phase transition in β-(BEDT-TTF)2I3 at around 125K, which was found earlier already in thermopower measurements, was observed in resistivity measurements. βt-(BEDT-TTF)2I3 crystals were prepared by annealing β-(BEDT-TTF)2I3 at 85 K for several weeks. The superconducting transition temperatures of the βt-(BEDT-TTF)2I3 crystals were found between 4.5K and 7K, that means at much higher temperatures than the observed Tc = 1.3K of β-(BEDT-TTF)2I3 crystals. Ac-susceptibility measurements indicate that the superconducting state is a bulk effect in βt-(BEDT-TTF)2I3.