Unconventional hysteresis due to time-reversal symmetry breaking superconductivity in RbV₃Sb₅

The study of kagome materials has recently attracted much attention due to the presence of many electron-electron interaction-driven phases in a single material. In this work, we report the time-reversal symmetry-breaking superconductivity in the thin-flake kagome material RbV₃Sb₅. Firstly, when an in-plane magnetic field is swept in opposite directions, we observe an unconventional form of hysteresis in magnetoresistance, which is different from the hysteresis induced by extrinsic mechanisms. In contrast, no such hysteresis is observed in CsV₃Sb₅ samples below their superconducting transition temperature. Strikingly, at a fixed magnetic field, the finite-resistance state in RbV₃Sb₅ can be transitioned into the superconducting state by applying and subsequently removing a large current. Secondly, at temperatures around 400 mK, the re-entrance of superconductivity occurs during an in-plane field-sweeping process with a fixed sweeping direction. The observations of the unconventional hysteresis and re-entrance suggest the existence of time-reversal symmetry-breaking superconducting states in RbV₃Sb₅.