Signatures of time-reversal-symmetry breaking in multiband 2H-TaS2 revealed by zero-field Josephson nonreciprocity

TL;DR

This study demonstrates zero-field Josephson diode effects and nonlinear Hall transport in 2H-TaS2, indicating multiband superconductivity with intrinsic time-reversal-symmetry breaking.

Contribution

It provides experimental evidence of time-reversal-symmetry breaking in a nominally isotropic superconductor through Josephson nonreciprocity and nonlinear Hall effects.

Findings

Zero-field Josephson diode effect observed in 2H-TaS2/2H-NbSe2 junctions.

Nonlinear Hall response in TaS2 consistent with multiband correlated states.

Modeling shows interband scattering induces an intrinsic phase difference leading to nonreciprocal supercurrent.

Abstract

Superconductors that spontaneously break time-reversal symmetry host complex order parameters and are widely regarded as a hallmark of unconventional superconductivity. Whether such symmetry breaking can also arise in superconductors with nominally isotropic spin-singlet pairing remains an open question. Here we report a zero-field Josephson diode effect in noncentrosymmetric 2H-TaS2/2H-NbSe2 van der Waals junctions. The diode efficiency shows no systematic correlation with supercurrent amplitude, TaS2 thickness, or normal-state resistance, arguing against simple extrinsic, purely interfacial, or transparency-driven mechanisms. Time-reversal-symmetric scenarios are further tested using symmetry-controlled and molecule-intercalated control devices, in which the nonreciprocal response is absent or strongly reduced. Normal-state Hall transport in TaS2 exhibits a nonlinear response consistent with multiband correlated electronic states. Within a Josephson framework, our modelling shows that interband scattering acts as a phase-locking mechanism generating an intrinsic anomalous phase difference and a nonsinusoidal asymmetric current-phase relation, leading to finite zero-field rectification. Together, zero-field Josephson nonreciprocity and nonlinear Hall transport provide complementary evidence for a multiband superconducting phase structure in 2H-TaS2, consistent with intrinsic time-reversal-symmetry breaking.