Mixed triplet-singlet order parameter in decoupled superconducting 1H monolayers of transition-metal dichalcogenides

Abstract

Abstract Understanding the emergence of unconventional superconductivity, where the order parameter deviates from simple isotropic s-wave pairing, is a central challenge in condensed matter physics. Some transition-metal dichalcogenides (TMDCs), though generally regarded as conventional superconductors, display signatures of unconventional pairing and thus provide a particularly intriguing platform to explore how exotic states arise. Here we investigate the misfit compound (SnS) 1.15 (TaS 2 ), a heterostructure composed of alternating SnS and 1H-TaS 2 layers. Using transport, photoemission, and scanning tunneling spectroscopy, we demonstrate that the SnS layers effectively decouple the TaS 2 into electronically isolated 1H sheets. In this limit, the tunneling density of states on the 1H layer reveals a clear two-gap superconducting spectrum with T c ≃ 3.1 K. A theoretical model based on lack of inversion symmetry of the system and finite-range attraction reproduces the observed multi-gap structure as a mixed singlet-triplet state. These results establish misfit compounds as a powerful platform for studying unconventional superconductivity in isolated 1H layers and for realizing multiple uncoupled superconductors within a single crystal.