Metallization and superconductivity with Tc > 12 K in transition metal dichalcogenide HfS2 under pressure

The application of high pressure not only drives the comprehension of the structure and triggers exotic electronic states in transition metal dichalcogenides, but also promotes the discovery of intriguing phenomena. Here, we show that HfS2 exhibits highly tunable electronic property under pressure with sequence of gradual narrowing of band-gap at <40 GPa, followed by pressure-induced metallization at above 40 GPa, and ultimately superconductivity starting at ∼115 GPa. Raman and x-ray diffraction experiments provide strong evidence for first-order structural phase transitions from a trigonal (P 3‾ m1) to an orthorhombic (Immm) at around 18 GPa and then to a tetragonal structure (I4/mmm) above 40 GPa. The disappearance of all the Raman modes supported the observed metallization at above 40 GPa. At the similar pressure, the carrier-type of the sample is found to transform from electron to hole according to the Hall coefficient. At a critical pressure of 115 GPa a superconducting state sets with a transition temperature (Tc) of 3 K. Further compression dramatically increases Tc up to a maximum value of 12.2 K at 173 GPa, setting a record of Tc for superconducting transition metal dichalcogenides with zero-resistance. The pressure-induced high Tc superconductivity is closely linked to structural reconstructions which trigger changes in electronic states near the Fermi surface. The efficient and remarkable manipulation on the transport properties of 1T-HfS2 not only shed lights on the broad perspective of layered materials but also provide crucial information towards their practical applications.