Superconductor-Insulator Phase Separation Induced by Rapid Cooling in kappa-(ET)2Cu[N(CN)2]Br

Abstract

We present measurements of the low temperature specific heat of single crystals of kappa-(ET)2Cu[N(CN)2]Br as a function of the cooling rate through the glasslike structure transition at 80K. We find that rapid cooling produces a small (< 4%) decrease in the superconducting transition temperature accompanied by a substantial (up to 50%) decrease in the normal-state electronic specific heat. A natural explanation of our data is that there is a macroscopic phase separation between superconducting and insulating regions in rapidly cooled samples.