Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating

Functionalities of two-dimensional (2D) crystals based on semiconducting transition metal dichalcogenides (TMDs) have now stemmed from simple field effect transistors (FETs) to a variety of electronic and opto-valleytronic devices, and even to superconductivity. Among them, superconductivity is the least studied property in TMDs due to methodological difficulty accessing it in different TMD species. Here, we report the systematic study of superconductivity in MoSe(2), MoTe(2) and WS(2) by ionic gating in different regimes. Electrostatic gating using ionic liquid was able to induce superconductivity in MoSe(2) but not in MoTe(2) because of inefficient electron accumulation limited by electronic band alignment. Alternative gating using KClO(4)/polyethylene glycol enabled a crossover from surface doping to bulk doping, which induced superconductivities in MoTe(2) and WS(2) electrochemically. These new varieties greatly enriched the TMD superconductor families and unveiled critical methodology to expand the capability of ionic gating to other materials.