Quantum oscillation and unusual protection mechanism of the surface state in nonsymmorphic semimetals

TL;DR

This study reports on a novel, topologically trivial surface state in nonsymmorphic semimetals that exhibits quantum oscillations and high mobility, revealing a new protection mechanism distinct from traditional topological surface states.

Contribution

It demonstrates the existence of a trivial yet protected surface band in nonsymmorphic semimetals, supported by quantum transport measurements in ZrSiSe flakes.

Findings

Observation of quantum oscillations in the surface state

Surface band exhibits high mobility despite trivial topology

Protection mechanism differs from conventional topological states

Abstract

In a topological semimetal with Dirac or Weyl points, the bulk edge correspondence principle predicts a gapless edge mode if the essential symmetry is still preserved at the surface. The detection of such topological surface state has been considered as the fingerprint prove for crystals with nontrivial topological bulk band. On the contrary, it has been proposed that even with symmetry broken at the surface, a new surface band can emerge in nonsymmorphic topological semimetals. The symmetry reduction at the surface lifts the bulk band degeneracies, produces an unusual floating surface band with trivial topology. Here, we report quantum transport probing to ZrSiSe thin flakes and reveal transport signatures of this new surface state. Remarkably, though topologically trivial, such a surface band exhibit substantial two dimensional Shubnikov de Haas quantum oscillations with high mobility, which signifies a new protection mechanism and may open applications for surface-related devices.