Pressure-tunable superconductivity in transition-metal dichalcogenides

Transition metal dichalcogenides (TMDs) are typical two-dimensional graphenelike layered structure materials. Compared with graphene’s all-carbon composition and bandgapfree electronic structure, TMDs have more abundant element composition, various crystal structure and novel physical properties. Their strong anisotropy and excellent performance in catalysis, photovoltaic devices and energy storage materials have aroused great interest of scientists. These layered structure TMDs are very sensitive to pressure due to their interlayer stacking mode and weak interlayer van der Waals forces, and it is easy to alter their crystal structure and electronic band under high pressure, and further to change the electronic ground state. they span a wealth of electronic ground states encompassing Mott insulators, excitonic insulators, charge density waves, semiconductors, (topological) semimetals, metals, and superconductors. Some pristine polymorphs can even exhibit intrinsic superconductivity at ambient pressure. Experiments show that extrinsic superconductivity can be induced or enhanced in a multitude of pristine polymorph TMDs via external pressure. In this review, the emergence and evolution of superconductivity in these polymorphs upon application of pressure is addressed.