Surface Floating 2D Bands in Layered Nonsymmorphic Semimetals: ZrSiS and Related Compounds

Andreas Topp,Raquel Queiroz,Maxim Krivenkov,Fanny Rodolakis,Bettina V Lotsch,Jessica L Mcchesney,Leslie M Schoop,Andrei Varykhalov,Andreas Grüneis,Lukas Müchler,Dmitry Marchenko,Andreas W Rost,Christian R Ast

doi:10.1103/physrevx.7.041073

Abstract

In this work, we present a model of the surface states of nonsymmorphic semimetals. These are derived from surface mass terms that lift the high degeneracy imposed in the band structure by the nonsymmorphic bulk symmetries. Reflecting the reduced symmetry at the surface, the bulk bands are strongly modified. This leads to the creation of two-dimensional floating bands, which are distinct from Shockley states, quantum well states or topologically protected surface states. We focus on the layered semimetal ZrSiS to clarify the origin of its surface states. We demonstrate an excellent agreement between DFT calculations and ARPES measurements and present an effective four-band model in which similar surface bands appear. Finally, we emphasize the role of the surface chemical potential by comparing the surface density of states in samples with and without potassium coating. Our findings can be extended to related compounds and generalized to other crystals with nonsymmorphic symmetries.

Highlights

Surface states have gained significant interest as they reflect both surface details and bulk properties
We propose that the surface states of ZrSiS are not derived from the nonsymmorphic bulk band topology, such as hourglass [36] and Dirac [37] surface states, nor are they due to a structural surface modification, but instead are the result of a reduced symmetry at the surface
We find that the origin of the surface states in ZrSiS and related compounds can be attributed to the symmetry reduction at the surface

Summary

INTRODUCTION

Surface states have gained significant interest as they reflect both surface details and bulk properties. We propose that the surface states of ZrSiS are not derived from the nonsymmorphic bulk band topology, such as hourglass [36] and Dirac [37] surface states, nor are they due to a structural surface modification, but instead are the result of a reduced symmetry at the surface. The energy gap separating surface and bulk bands originates from the unpinning of bands along the XM line, as the symmetry enforced degeneracies are locally lifted, but remain pinned in the bulk. Such a symmetryderived surface electronic structure does not fit any of the aforementioned surface state models, and is not particular to this space group.

METHODS

SURFACE STATE

SYMMETRIES AND EFFECTIVE MODEL

RESPONSE TO SURFACE MODIFICATION

Findings

DISCUSSION AND CONCLUSION