At ambient pressure, HfTe5 is a material at the boundary between a weak and a strong topological phase, which can be tuned by changes in its crystalline structure or by the application of high magnetic fields. It exhibits a Lifshitz transition upon cooling, and three-dimensional (3D) quantum Hall effect (QHE) plateaus can be observed at low temperatures. Here, we have investigated the electrical transport properties of HfTe5 under hydrostatic pressure up to 3 GPa. We find a pressure-induced crossover from a semimetallic phase at low pressures to an insulating phase at about 1.5 GPa. Our data suggest the presence of a pressure-induced Lifshitz transition at low temperatures within the insulating phase around 2 GPa. The quasi-3D QHE is confined to the low-pressure region in the semimetallic phase. This reveals the importance of the semimetallic groundstate for the emergence of the QHE in HfTe5 and thus favors a scenario based on a low carrier density metal in the quantum limit for the observed signatures of the quasi-quantized 3D QHE.
@article{arxiv.2404.13969,
title = {Importance of the semimetallic state for the quantum Hall effect in HfTe$_{5}$},
author = {M. M. Piva and R. Wawrzyńczak and Nitesh Kumar and L. O. Kutelak and G. A. Lombardi and R. D. dos Reis and C. Felser and M. Nicklas},
journal= {arXiv preprint arXiv:2404.13969},
year = {2024}
}