kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br: a Fully Gapped Strong-Coupling Superconductor

TL;DR

This study demonstrates that the organic superconductor kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br has a fully gapped order parameter consistent with strong-coupling BCS theory, based on high-resolution specific heat measurements.

Contribution

It provides experimental evidence that this organic superconductor is a fully gapped, strong-coupling superconductor, supporting BCS theory predictions.

Findings

Electronic specific heat vanishes exponentially below Tc

Superconducting gap is fully open with no nodes

Strong-coupling BCS theory describes the data well

Abstract

High-resolution specific-heat measurements of the organic superconductor kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br in the superconducting (B = 0) and normal (B = 14 T) state show a clearly resolvable anomaly at Tc = 11.5 K and an electronic contribution, Ces, which can be reasonably well described by strong-coupling BCS theory. Most importantly, Ces vanishes exponentially in the superconducting state which gives evidence for a fully gapped order parameter.