Revealing a charge-density-wave gap in the predicted weak topological insulator HoSbTe

HoSbTe was predicted to be a weak topological insulator whose spin-orbit coupling (SOC) gaps are reported to be as large as hundreds of meV. Utilizing infrared spectroscopy, we find that the compound has a metallic nature from 350 down to 10 K. Particularly, both its itinerant carrier density and scattering rate are demonstrated to decrease with temperature cooling, which is responsible for the appearance of a broad hump feature in the temperature-dependent resistivity around 200 K. More importantly, we reveal the appearance of a charge-density-wave (CDW) gap whose energy scale is identified to shift from 364 meV at 10 K to 252 meV at 350 K. An SOC-induced band splitting is observed as well, and its coexistence with the CDW gap in the same compound paves the way to explore more intriguing physics.