Time-reversal symmetry breaking in the superconducting state of ScS

Abstract

We have studied the electronic properties of ScS, a transition-metal monochalcogenide with a rocksalt crystal structure, using magnetization, specific heat, transport, and muon spin rotation/relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements. All measurements confirm the bulk superconductivity in ScS with a transition temperature of ${T}_{C}=5.1(5)$ K. Specific heat together with transverse-field $\ensuremath{\mu}\mathrm{SR}$ measurements indicate a full gap, while our zero-field $\ensuremath{\mu}\mathrm{SR}$ study reveals the presence of spontaneous static or quasistatic magnetic fields emerging when entering the superconducting state. We discuss various possible microscopic origins of the observed time-reversal symmetry breaking. As none of them can be readily reconciled with a conventional pairing mechanism, this introduces ScS as a candidate material for unconventional superconductivity.