Broken Screw Rotational Symmetry in the Near-Surface Electronic Structure of $AB$-Stacked Crystals

TL;DR

This study reveals that near-surface electronic structures of certain layered materials can differ significantly from their bulk properties due to broken symmetries, as demonstrated through ARPES experiments and first-principles calculations.

Contribution

It provides evidence that nonsymmorphic symmetries can be partially broken at surfaces, affecting the electronic structure observed in ARPES measurements.

Findings

Near-surface electronic structures show gapped dispersions unlike bulk expectations.

First-principles calculations reproduce the gapped ARPES spectra.

Broken symmetries at the surface alter electronic properties.

Abstract

We investigate the electronic structure of $2H$-$\mathrm{Nb}\mathrm{S}_2$ and $h$-$\mathrm{BN}$ by angle-resolved photoemission spectroscopy (ARPES) and photoemission intensity calculations. Although in bulk form, these materials are expected to exhibit band degeneracy in the $k_z=\pi/c$ plane due to screw rotation and time-reversal symmetries, we observe gapped band dispersion near the surface. We extract from first-principles calculations the near-surface electronic structure probed by ARPES and find that the calculated photoemission spectra from the near-surface region reproduce the gapped ARPES spectra. Our results show that the near-surface electronic structure can be qualitatively different from the bulk one due to partially broken nonsymmorphic symmetries.