Unveiling the pressure-driven metal–semiconductor–metal transition in the doped TiS_(2)

Conventional theories expect that materials under pressure exhibit expanded valence and conduction bands,leading to increased electrical conductivity.Here,we report the electrical properties of the doped 1T-TiS_(2) under high pressure by electrical resistance investigations,synchrotron x-ray diffraction,Raman scattering and theoretical calculations.Up to 70 GPa,an unusual metal-semiconductor-metal transition occurs.Our first-principles calculations suggest that the observed anti-Wilson transition from metal to semiconductor at 17 GPa is due to the electron localization induced by the intercalated Ti atoms.This electron localization is attributed to the strengthened coupling between the doped Ti atoms and S atoms,and the Anderson localization arising from the disordered intercalation.At pressures exceeding 30.5 GPa,the doped TiS_(2) undergoes a re-metallization transition initiated by a crystal structure phase transition.We assign the most probable space group as P2_(1)2_(1)2_(1).Our findings suggest that materials probably will eventually undergo the Wilson transition when subjected to sufficient pressure.

Re-emergence of superconductivity via pressure-induced Lifshitz transition in preserved 6R-TaS_(2) crystal structure

Investigating the implications of interlayer coupling on superconductivity is vital for comprehending the intrinsic mechanisms of two-dimensional materials.Van der Waals heterojunctions have attracted extensive research owing to their exotic interlayer coupling.In this study,we investigated the natural heterostructure superconductor featuring 6R-TaS_(2) via measurements of electrical resistance,the Hall effect,and in-situ synchrotron X-ray diffraction(XRD)under various pressures.The study findings show that the superconducting transition temperature(T_(c))of 6R-TaS_(2) in the range of 0-32.5 GPa exhibits an unusual double-dome behavior as a function of pressure,with the first and second domes in the pressure range of 0-5.3 and 6.8-32.5 GPa,respectively.At 56.6GPa,a new superconducting phase with a T_(c) of 2 K was observed.The XRD results show that the singular evolution of the T_(c) is independent of the structural phase transition.Combining the XRD results,first-principles calculations,and Hall effect measurements,we found that different interlayer coupling effects resulted in double dome superconductivity and the re-emergence of superconducting.Our findings shed light on the pivotal role of interlayer coupling in driving the anomalous alterations in superconducting properties triggered by charge transfer and Fermi surface reconstruction and provide an alternative route for comprehending the mechanisms of superconductivity in transition metal dichalcogenides(TMDs).