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

I Marković,P A E Murgatroyd,P D C King,F Mazzola,P Le Fèvre,S Wu,M S Dyer,K Underwood,C A Hooley,O J Clark,K J Murphy,K Volckaert,J Alaria,I Vobornik,F Bertran,T Okuda,M D Watson,J Fujii,J M Riley

doi:10.1038/s41467-019-13464-z

Abstract

Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states 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 near the Fermi level in NbGeSb, and to develop pronounced 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.

Highlights

Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals
We demonstrate how the enhanced spin-orbit coupling leads to the development of pronounced Rashba-like spin splittings and show, both experimentally and via ab initio calculations, how this leads to a rich crossing structure of the spinpolarised surface states
The above findings illustrate how surface states, as well as bulk states, can provide a rich environment for realising, and extending, the rich variety of electronic structures that can be generated from band inversions in solids, opening new opportunities to profit from the different symmetries and environment of the surface itself

Summary

Introduction

Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals. When its nonsymmorphic symmetry is broken at the crystal surface, new sets of electronic states are created, split off from the bulk manifold[8] One such surface state, SS, of dominantly Zr character, intersects the Fermi another, SS0, of predominantly S character, is level (EF), located at while much higher binding energies[8,20]. We find how oppositely polarised states hybridise where they cross, but exhibit a large and unusual asymmetry in the scale of their hybridisation gaps, while protected, Weyl-like points are formed at the crossings of like-spin bands We show how this results from the coupled spin-angular and orbital-angular momentum texture of these states, and demonstrate a critical role of mirror symmetry in the surface plane

Methods

Results

Conclusion