Ising superconductivity and Majorana fermions in transition-metal dichalcogenides

TLDR

A monolayer of transition metal dichalcogenides has a noncentrosymmetric lattice that gives rise to Ising spin–orbit coupling, which pins electron spins out‑of‑plane and strongly enhances the in‑plane upper critical field of its superconducting state. The authors aim to show that this Ising SOC can induce spin‑triplet Cooper pairing with in‑plane spin orientation, leading to a topological superconducting state in spin‑polarized proximity‑coupled wires and generating Majorana end states. They demonstrate that the resulting Majorana states are more experimentally accessible because the strong Ising SOC expands the topologically nontrivial regime.

Abstract

Due to its noncentrosymmetric lattice structure, a monolayer of transition metal dichalcogenides (TMD) possesses a very special type of spin-orbit coupling (SOC) called Ising SOC. Unlike Rashba SOC, Ising SOC pins electron spins to the out-of-plane rather than the in-plane direction. In TMD materials, the Ising SOC is quite strong and substantially enhances the in-plane upper critical field of their superconducting state. Despite this, the authors show here that the Ising SOC can in fact lead to spin-triplet Cooper pairing with electrons spins pointing in the in-plane direction. Such pairing induces a topological superconducting state in spin-polarized proximity coupled wires and generates Majorana end states. So-formed Majorana states can be more accessible experimentally due to the strong Ising SOC and a wider topologically nontrivial regime.