Two superconducting phases in the organic conductor: β-(BEDT-TTF)2I3

Abstract

We have investigated the nature and the stability of the high-Tc(∼8 K) and low-Tc (∼1.5 K)superconducting phases (respectively called β-H and β-L) of the organic conductor β-(BEDT-TTF)2I3. First, by resistivity measurements and following a well-defined temperature-pressure cycling process, we show that the β-H phase is stabilized at ambient pressure and low temperature, exhibiting a very sharp and complete superconducting transition at 8.1 K and 1 bar. Secondly, an AC-susceptibility study reveals that this state is stable and exhibits bulk superconductivity at high Tc and ambient P as long as the sample is not warmed above 125 K. Finally, we present NMR results on the 1H spin-lattice relaxation rate behaviour in both the β-H phase and the β-L phase.