Temperature-induced Lifshitz transition in topological insulator candidate HfTe.

The ongoing discoveries and studies of novel topological quantum materials have become an emergent and important field of condensed matter physics. Recently, HfTe ignited renewed interest as a candidate of a novel topological material. The single-layer HfTe 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, HfTe 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 HfTe. Our results indicated that a temperature-induced Lifshitz transition occurs in HfTe, which provides a natural understanding on the origin of the transport anomaly in HfTe. In addition, our observations suggest that HfTe is a weak topological insulator that is located at the phase boundary between weak and strong topological insulators at very low temperature.