Time-reversal-breaking Pair-mixing States in Transition Metal Dichalcogenides Superconductors

Experimental evidence of spontaneous time-reversal (TR) symmetry breaking has been reported for the superconducting ground state in the transition metal dichalcogenides (TMD) superconductor 4H_b-TaS₂ or chiral molecule intercalated TaS₂ hybrid superlattices, and is regarded as the evidence of the emergent chiral superconductivity. However, the T_c  of these TMD superconductors is at the same order as pristine 1H or 2H-TaS₂ that does not show any signature of TR breaking and is believed to be a conventional Bardeen–Cooper–Schrieffer superconductors. To resolve this puzzle, we proposed a new type of pair-mixing states that mix the dominant conventional s-wave pairing channel with the subdominant chiral p-wave pairing channel via the finite Cooper pair momentum based on the symmetry analysis of the Ginzburg-Landau theory for these superconductors. Particularly, our analysis shows the fourth order terms in the chiral channel can spontaneously break TR symmetry for a variety of pair-mixing states. These TR-breaking superconducting states also reveal zero-field superconducting diode effect that is observed in chiral molecule intercalated TaS₂ superlattices.