Temperature-induced Lifshitz transition in topological insulator candidate HfTe₅

The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics. Recently, HfTe₅ ignited renewed interest as a candidate of a novel topological material. The single-layer HfTe₅ is predicted to be a two-dimensional large band gap topological insulator and can be stacked into a bulk that may host a temperature-driven topological phase transition. Historically, HfTe₅ attracted considerable interest for its anomalous transport properties characterized by a peculiar resistivity peak accompanied by a sign reversal carrier type. The origin of the transport anomaly remains under a hot debate. Here we report the first high-resolution laser-based angle-resolved photoemission measurements on the temperature-dependent electronic structure in HfTe₅. Our results indicated that a temperature-induced Lifshitz transition occurs in HfTe₅, which provides a natural understanding on the origin of the transport anomaly in HfTe₅. In addition, our observations suggest that HfTe₅ is a weak topological insulator that is located at the phase boundary between weak and strong topological insulators at very low temperature.