Topological Lifshitz transition and one-dimensional Weyl mode in HfTe5

TL;DR

This study reveals a topological Lifshitz transition and the emergence of one-dimensional Weyl modes in HfTe5 under high magnetic fields, demonstrating a new route to realize Weyl quasiparticles in bulk materials.

Contribution

The paper reports the first observation of a topological Lifshitz transition and 1D Weyl modes in HfTe5 driven by magnetic field-induced band inversion.

Findings

Band inversion causes Landau level crossing at 4.5 T.

Topological Lifshitz transition occurs at 21 T.

Emergence of a broad, asymmetric absorption feature and negative magneto-resistivity.

Abstract

Landau band crossings typically stem from the intra-band evolution of electronic states in magnetic fields and enhance the interaction effect in their vicinity. Here in the extreme quantum limit of topological insulator HfTe5, we report the observation of a topological Lifshitz transition from inter-band Landau level crossings using magneto-infrared spectroscopy. By tracking the Landau level transitions, we demonstrate that band inversion drives the zeroth Landau bands to cross with each other after 4.5 T and forms one-dimensional Weyl mode with fundamental gap persistently closed. The unusual reduction of the zeroth Landau level transition activity suggests a topological Lifshitz transition at 21 T which shifts the Weyl mode close to Fermi level. As a result, a broad and asymmetric absorption feature emerges due to the Pauli blocking effect in one dimension, along with a distinctive negative magneto-resistivity. Our results provide a strategy for realizing one-dimensional Weyl quasiparticles in bulk crystals.