Pair-mixing induced Time-reversal-breaking superconductivity

TL;DR

This paper proposes a new pair-mixing superconducting state combining s-wave and chiral p-wave channels with finite momentum, explaining spontaneous time-reversal symmetry breaking and diode effects in TMD superconductors.

Contribution

It introduces a novel pair-mixing state theory that accounts for TR breaking and diode effects in TMD superconductors, resolving existing experimental puzzles.

Findings

Identification of a new pair-mixing state with TR breaking.

Prediction of a superconducting diode effect in chiral TMD superlattices.

Explanation of TR symmetry breaking in TMD superconductors.

Abstract

Experimental evidences of spontaneous time-reversal (TR) symmetry breaking have been reported for the superconducting ground state in the transition metal dichalcogenide (TMD) superconductor 4H$_b$-TaS$_2$ or chiral molecule intercalated TaS$_2$ hybrid superlattices, and is regarded as evidence of emergent chiral superconductivity. However, the $T_c$ of these TMD superconductors is of the same order as pristine 1H or 2H-TaS$_2$, which do not show any signature of TR breaking and are believed to be conventional Bardeen-Cooper-Schrieffer superconductors. To resolve this puzzle, we propose a new type of pair-mixing state that mixes the dominant conventional s-wave pairing channel with the subdominant chiral p-wave pairing channel via a finite Cooper-pair momentum, based on symmetry analysis within the Ginzburg-Landau theory. Our analysis shows that the fourth-order terms in the chiral p-wave channel can lead to a variety of pair-mixing states with spontaneous TR breaking. These TR-breaking superconducting states also reveal a zero-field, junction-free superconducting diode effect that is observed in chiral molecule intercalated TaS$_2$ superlattices.