Nodal Superconducting Gap in $\beta$-FeS

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.

6 pages, 5 figures

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