Time-reversal-symmetry Breaking in the Superconducting State of ScS

We have studied the electronic properties of ScS, a transition-metal monochalcogenide with rocksalt crystal structure, using magnetization, specific heat, transport, and muon spin rotation/relaxation ($\mu$SR) measurements. All measurements confirm the bulk superconducting in ScS with a transition temperature of $T_{C}$ = 5.1(5) K. Specific heat together with transverse-field $\mu$SR measurements indicate a full gap, while our zero-field $\mu$SR study reveals the presence of spontaneous static or quasi-static 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 novel candidate material for unconventional superconductivity.