Superconductor-Insulator Phase Separation Induced by Rapid Cooling in kappa-(ET)_2Cu[N(CN)_2]Br

TL;DR

This study shows that rapid cooling of kappa-(ET)_2Cu[N(CN)_2]Br causes phase separation into superconducting and insulating regions, significantly affecting its electronic properties at low temperatures.

Contribution

It provides experimental evidence linking cooling rate to phase separation and electronic property changes in this organic superconductor.

Findings

Rapid cooling decreases superconducting transition temperature by less than 4%.

Normal-state electronic specific heat decreases by up to 50% with rapid cooling.

Phase separation between superconducting and insulating regions is induced by rapid cooling.

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 $\sim$ 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.