Location of gap nodes in the organic superconductors $\kappa$-(ET)$_2$Cu(NCS)$_2$ and $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br determined by magnetocalorimetry

TL;DR

This study uses magnetocalorimetry to identify the location of gap nodes in organic superconductors, revealing a fourfold symmetry consistent with d_{xy} gap structure, advancing understanding of their pairing symmetry.

Contribution

It provides direct experimental evidence of the gap node locations in specific organic superconductors using magnetocalorimetry, a novel approach for this purpose.

Findings

Detected fourfold oscillations in specific heat indicating gap nodes.

Confirmed nodes point along in-plane crystal axes, consistent with d_{xy} symmetry.

Demonstrated field and temperature dependence of the oscillations.

Abstract

We report specific heat measurements of the organic superconductors $\kappa$-(ET)$_2$Cu(NCS)$_2$ and $\kappa$-(ET)$_2$Cu[N(CN)$_2$]Br. When the magnetic field is rotated in the highly conducting planes at low temperature ($T\simeq 0.4$ K), we observe clear oscillations of specific heat which have a strong fourfold component. The observed strong field and temperature dependence of this fourfold component identifies it as originating from nodes in the superconducting energy gap which point along the in-plane crystal axes ($d_{xy}$ symmetry)