Upper critical field in few-layer Ising superconductors

TL;DR

This paper investigates the upper critical magnetic field in few-layer Ising superconductors, emphasizing the importance of Fermi surface pockets, proposing an experiment to determine spin-symmetry, and exploring mixed-parity order parameters.

Contribution

It introduces a comprehensive analysis of the upper critical field considering all Fermi surface pockets and proposes experimental methods to identify spin-symmetry in multilayer Ising superconductors.

Findings

Scaling of the upper critical field varies with displacement field in bilayers.

Fermi surface pockets are essential for accurate critical field predictions.

Mixed-parity order parameters may exhibit dominant spin-singlet scaling.

Abstract

The N-layer 2H-stacked transition metal dichalcogenides 2H-NbSe2 and 2H-TaS2 are superconductors in which each quasi-two-dimensional layer breaks inversion symmetry. In this paper, we show that, as for the individual monolayers, it is crucial to include all pockets at the Fermi surface to accurately determine the upper critical field. Furthermore, we propose an experiment where a distinct scaling with a varying displacement field is predicted for an intralayer spin-singlet order in a bilayer. The scaling of the upper critical field with external tuning parameters can thus be used to extract information about the spin-symmetry of the superconducting order. We also explore the possibility of a mixed-parity spin-singlet and -triplet order parameter. In that case, we predict that the experimentally observable scaling would remain that of the spin-singlet component.