Nodal Superconducting Gap in $\beta$-FeS

TL;DR

This study investigates the superconducting gap structure of $eta$-FeS, revealing evidence for nodal gaps through specific heat measurements and magnetic field dependence, challenging the conventional s-wave pairing model.

Contribution

The paper provides experimental evidence for nodal superconducting gaps in $eta$-FeS, using specific heat data and magnetic field analysis, which is a novel insight into its pairing symmetry.

Findings

Low temperature electronic specific heat fits a linear relation.

Fails to fit exponential s-wave gap model.

Field-induced specific heat follows Volovik relation, indicating nodal gaps.

Abstract

Low temperature specific heat has been measured in superconductor $\beta$-FeS with T$_c$ = 4.55 K. It is found that the low temperature electronic specific heat C$_e$/T can be fitted to a linear relation in the low temperature region, but fails to be described by an exponential relation as expected by an s-wave gap. We try fittings to the data with different gap structures and find that a model with one or two nodal gaps can fit the data. Under a magnetic field, the field induced specific heat $\Delta\gamma$=[C$_e$(H)-C$_e$(0)]/T shows the Volovik relation $\Delta\gamma_e(H)\propto \sqrt{H}$, suggesting the presence of nodal gap(s) in this material.