Abstract
ZrTe5 and HfTe5 have attracted increasingly attention recently since the theoretical prediction of being topological insulators (TIs). However, subsequent works show many contradictions about their topolog-ical nature. Three possible phases, i.e. strong TI, weak TI, and Dirac semi-metal, have been observed in different experiments until now. Essentially whether ZrTe5 or HfTe5 has a band gap or not is still a question. Here, we present detailed first-principles calculations on the electronic and topological prop-erties of ZrTe5 and HfTe5 on variant volumes and clearly demonstrate the topological phase transition from a strong TI, going through an intermediate Dirac semi-metal state, then to a weak TI when the crystal expands. Our work might give a unified explain about the divergent experimental results and propose the crucial clue to further experiments to elucidate the topological nature of these materials.
Highlights
ZrTe5 and HfTe5 have attracted increasingly attention recently since the theoretical prediction of being topological insulators (TIs)
We can conclude that the electronic properties of ZrTe5 (HfTe5) are very sensitive to the change of the volume and they are located very close to the boundary between the strong and weak TI
Our optimized and the experimentally measured volume of ZrTe5 (HfTe5) both indicate that they should be within the strong TI region, we think it still has the possibility that ZrTe5 (HfTe5) can locate in a weak TI region due to different growth methods and characterization techniques in experiments
Summary
ZrTe5 and HfTe5 have attracted increasingly attention recently since the theoretical prediction of being topological insulators (TIs). In two recent scanning tunneling microscopy (STM) experiments, they unambiguously observed a large bulk band gap about 80 or 100 meV in ZrTe516,17, implying that there is no surface state on the top surface and ZrTe5 should be a weak TI. By using the comprehensive ARPES, STM, and first principles calculations, Manzoni et al found a metallic density of state (DOS) at Fermi energy, which arises from the two-dimensional surface state and indicates ZrTe5 is a strong TI19 The divergence of these experiments make ZrTe5 (HfTe5) being a very puzzling but interesting material, which needs more further experimental and theoretical studies. This work could shed more light on a unified explain about the different experimental results, and propose the crucial clue to further experiments to elucidate the topological nature of ZrTe5 and HfTe5
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