Robustness and Universality of Surface States in Dirac Materials

TL;DR

This paper reveals a non-topological mechanism for creating robust, propagating surface states in Dirac materials, which resemble topological states but do not require topological protection or crystal symmetries.

Contribution

It introduces a novel, non-topological origin of surface states in Dirac materials, expanding understanding of their robustness and transport properties.

Findings

Surface states can be generated without topological restrictions.

Surface states exhibit gate-tunable dispersion regimes.

These states are weakly affected by surface disorder.

Abstract

Ballistically propagating topologically protected states harbor exotic transport phenomena of wide interest. Here we describe a nontopological mechanism that produces such states at the surfaces of generic Dirac materials, giving rise to propagating surface modes with energies near the bulk band crossing. The robustness of surface states originates from the unique properties of Dirac-Bloch wavefunctions which exhibit strong coupling to generic boundaries. Surface states, described by Jackiw-Rebbi-type bound states, feature a number of interesting properties. Mode dispersion is gate tunable, exhibiting a wide variety of different regimes, including nondispersing flat bands and linear crossings within the bulk bandgap. The ballistic wavelike character of these states resembles the properties of topologically protected states; however, it requires neither topological restrictions nor additional crystal symmetries. The Dirac surface states are weakly sensitive to surface disorder and can dominate edge transport at the energies near the Dirac point.