Magnetic Field Driven Nodal Topological Superconductivity in Monolayer Transition Metal Dichalcogenides

TL;DR

This paper predicts that monolayer transition metal dichalcogenides like NbSe₂ and TaS₂ can become nodal topological superconductors with Majorana flat bands under certain magnetic fields, offering a feasible way to realize Majorana fermions.

Contribution

It demonstrates that monolayer NbSe₂ and TaS₂ can host nodal topological superconductivity with Majorana flat bands under experimentally accessible magnetic fields.

Findings

Nodal points appear on the Γ-M lines where Ising SOC vanishes.

Majorana flat bands connect the bulk nodal points.

Zero energy Majorana modes induce spin-triplet Cooper pairs.

Abstract

Recently, Ising superconductors which possess in-plane upper critical fields much larger than the Pauli limit field are under intense experimental study. Many monolayer or few layer transition metal dichalcogenides are shown to be Ising superconductors. In this work, we show that in a wide range of experimentally accessible regimes where the in-plane magnetic field is higher than the Pauli limit field but lower than $H_{c2}$, a 2H-structure monolayer NbSe$_2$ or simiarly TaS$_2$ becomes a nodal topological superconductor. The bulk nodal points appear on the $\Gamma- M$ lines of the Brillouin zone where the Ising SOC vanishes. The nodal points are connected by Majorana flat bands, similar to the Weyl points being connected by surface Fermi arcs in Weyl semimetals. The Majorana flat bands are associated with a large number of zero energy Majorana fermion edge modes which induce spin-triplet Cooper pairs. This work demonstrates an experimentally feasible way to realise Majorana fermions in nodal topological superconductor, without any fining tuning of experimental parameters.