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.
@article{arxiv.2201.06022,
title = {Topological Lifshitz transition and one-dimensional Weyl mode in HfTe5},
author = {Wenbin Wu and Zeping Shi and Yuhan Du and Yuxiang Wang and Fang Qin and Xianghao Meng and Binglin Liu and Yuanji Ma and Zhongbo Yan and Mykhaylo Ozerov and Cheng Zhang and Hai-Zhou Lu and Junhao Chu and Xiang Yuan},
journal= {arXiv preprint arXiv:2201.06022},
year = {2023}
}