Inherited Weak Topological Insulator Signatures in Topological Hourglass Semimetal Nb3XTe6 (X = Si, Ge)

TL;DR

This study uncovers a novel topological phase in Nb3XTe6 materials, combining weak topological insulator features with hourglass semimetal characteristics, driven by nonsymmorphic symmetry and spin-orbit coupling.

Contribution

It reveals a new topological state in van der Waals materials that integrates weak TI and hourglass semimetal properties, supported by experimental and first-principles evidence.

Findings

Identification of bulk band inversion and spin-polarized surface states.

Observation of hourglass fermions and multi nodal chains.

Topological state protected by nonsymmorphic symmetry.

Abstract

Using spin-resolved and angle-resolved photoemission spectroscopy and first-principles calculations, we have identified bulk band inversion and spin polarized surface state evolved from a weak topological insulator (TI) phase in van der Waals materials Nb3XTe6 (X = Si, Ge). The fingerprints of weak TI homologically emerge with hourglass fermions, as multi nodal chains composed by the same pair of valence and conduction bands gapped by spin orbit coupling. The novel topological state, with a pair of valence and conduction bands encoding both weak TI and hourglass semimetal nature, is essential and guaranteed by nonsymmorphic symmetry. It is distinct from TIs studied previously based on band inversions without symmetry protections.