Discovery of a weak topological insulating state and van Hove singularity in triclinic RhBi2

TL;DR

This paper reports the discovery of a weak topological insulator state in RhBi2, featuring topological surface states with a van Hove singularity near the Fermi energy, highlighting its potential for novel quantum phenomena.

Contribution

The study identifies a weak topological insulator in RhBi2 within the P1 space group, with detailed ARPES and DFT analysis revealing unique surface states and a van Hove singularity.

Findings

Discovery of WTI state in RhBi2

Topological surface states with saddle points near Dirac point

Presence of van Hove singularity close to Fermi energy

Abstract

Time reversal symmetric (TRS) invariant topological insulators (TIs) fullfil a paradigmatic role in the field of topological materials, standing at the origin of its development. Apart from TRS protected 'strong' TIs, it was realized early on that more confounding weak topological insulators (WTI) exist. WTIs depend on translational symmetry and exhibit topological surface states only in certain directions making it significantly more difficult to match the experimental success of strong TIs. We here report on the discovery of a WTI state in RhBi2 that belongs to the optimal space group P1, which is the only space group where symmetry indicated eigenvalues enumerate all possible invariants due to absence of additional constraining crystalline symmetries. Our ARPES, DFT calculations, and effective model reveal topological surface states with saddle points that are located in the vicinity of a Dirac point resulting in a van Hove singularity (VHS) along the (100) direction close to the Fermi energy. Due to the combination of exotic features, this material offers great potential as a material platform for novel quantum effects.