Weyl-like points from band inversions of spin-polarised surface states in NbGeSb

TL;DR

This paper demonstrates how band inversions between surface states in NbGeSb create Weyl-like points, revealing new ways to engineer topological surface states through surface band inversions.

Contribution

It introduces a novel surface state band inversion mechanism in NbGeSb, leading to Weyl-like points stabilized by mirror symmetry, expanding topological state engineering.

Findings

Surface state band crossings are driven near the Fermi level.

Pronounced spin-orbit mediated spin splittings are observed.

Mirror symmetry protects crossing points in the surface band structure.

Abstract

Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states in inverted bulk band gaps of topological insulators to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals. Here, we create a band inversion not of bulk states, but rather between manifolds of surface states. We realise this by aliovalent substitution of Nb for Zr and Sb for S in the ZrSiS family of nonsymmorphic semimetals. Using angle-resolved photoemission and density-functional theory, we show how two pairs of surface states, known from ZrSiS, are driven to intersect each other in the vicinity of the Fermi level in NbGeSb, as well as to develop pronounced spin-orbit mediated spin splittings. We demonstrate how mirror symmetry leads to protected crossing points in the resulting spin-orbital entangled surface band structure, thereby stabilising surface state analogues of three-dimensional Weyl points. More generally, our observations suggest new opportunities for engineering topologically and symmetry-protected states via band inversions of surface states.