Superconducting properties of transition metal dichalcogenides in proximity to a conventional superconductor

TL;DR

This study models the superconducting behavior of transition metal dichalcogenides (TMDs) near conventional superconductors, revealing complex hybridization gaps and the emergence of spin-triplet pairs due to Ising and Rashba spin-orbit couplings.

Contribution

It introduces a detailed three-orbital model for TMDs in proximity to superconductors, highlighting the formation of hybridization gaps and mixed spin-triplet pairing induced by spin-orbit interactions.

Findings

Hybridization gaps at multiple energies due to multiorbital effects

Ising spin-orbit coupling induces spin splitting and triplet correlations

Rashba coupling generates equal spin-triplet pairs competing with mixed triplet states

Abstract

Transition metal dichalcogenides (TMDs) hold relevance for spin-triplet superconducting phases due to their inherent Ising spin-orbit coupling, but the majority of studies have so far focused on oversimplified models. In this work, we consider a TMD monolayer using a three-orbital model with anisotropic couplings and investigate the emergent superconducting properties when it is placed in proximity to a conventional spin-singlet $s$-wave superconductor. We find that the multiorbital nature of the TMDs lead to superconducting gaps not only at zero energy, but also at higher energies, so-called hybridization gaps, which exhibit a complex structure due to the anisotropic couplings, challenging their spectral measurement. Moreover, we find that the inherent Ising spin-orbit coupling induces a spin splitting and a spin polarization along the $z$-direction, which correlates with the emergence of mixed spin-triplet superconducting pairs. These spin-triplet pair correlations appear in the monolayer as a proximity-induced effect due to the impact of the Ising spin-orbit field on conventional spin-singlet $s$-wave superconductivity. Taking realistic parameters for a $\text{MoS}_2$ monolayer, we show that the Ising field is strong enough to induce spin-triplet pair correlations of the same magnitude as their spin-singlet counterparts. We also include Rashba spin-orbit coupling, naturally emerging in a heterostructure and find that it induces equal spin-triplet superconducting pairs that compete with the mixed spin-triplet pairs induced by the Ising spin-orbit coupling. Our findings help understand the superconducting properties of TMDs in proximity to conventional superconductors.