Superconductivity in HfS₂ at ultrahigh pressure

Adjusting the electrical and optical properties of two-dimensional materials by pressure is an important method to realize their applications in the fields of electronics and optoelectronic devices. Here, we report the highly tunable transport properties of the layered semiconductor HfS2 under high pressure, including metallization and superconducting transition. HfS2 is one of the IVB group transition-metal dichalcogenides, exhibiting a large band gap in ambient condition. The bandgap decreases from similar to 2.0 to similar to 1.1 eV within 15 GPa by pressure tuning, and HfS2 becomes metallic at -60 GPa. Moreover, a superconducting transition is observed under similar to 126 GPa, and the superconducting critical temperature (Tc) increases with further compression, reaching similar to 4.4 K at similar to 153 GPa. Hall-effect measurements show that pressure changes the carrier-concentration type from electron dominated to hole dominated at similar to 145 GPa. Two structural transitions are found at moderate pressure, and one of them agrees with the changes observed in absorption and Raman spectroscopy measurements. Manipulation of the transport and optical properties of HfS2 by pressure provides important information for its practical applications.