Nodal and nematic superconducting phases in NbSe2 monolayers from competing superconducting channels

TL;DR

This study investigates the complex superconducting phases in NbSe2 monolayers, revealing nodal and nematic states arising from competing channels, with experimental evidence of their symmetry properties and topological nature.

Contribution

It provides experimental and theoretical evidence for nodal topological and nematic superconducting phases in NbSe2 monolayers originating from multiple competing superconducting channels.

Findings

Six-fold nodal symmetry observed in Hc2 measurements

Agreement with theoretical predictions of topological superconducting phase

Unconventional superconducting states arise from competing channels

Abstract

Transition metal dichalcogenides like 2H-NbSe2 in their two-dimensional (2D) form exhibit Ising superconductivity with the quasiparticle spins are firmly pinned in the direction perpendicular to the basal plane. This enables them to withstand exceptionally high magnetic fields beyond the Pauli limit for superconductivity. Using field-angle-resolved magnetoresistance experiments for fields rotated in the basal plane we investigate the field-angle dependence of the upper critical field (Hc2), which directly reflects the symmetry of the superconducting order parameter. We observe a six-fold nodal symmetry superposed on a two-fold symmetry. This agrees with theoretical predictions of a nodal topological superconducting phase near Hc2, together with a nematic superconducting state. We demonstrate that in NbSe2 such unconventional superconducting states can arise from the presence of several competing superconducting channels.