Atomically thin films of layered materials such as molybdenum disulfide (MoS2) are of growing interest for the study of phase transitions in two-dimensions through electrostatic doping. Electrostatic doping techniques giving access to high carrier densities are needed to achieve such phase transitions. Here we develop a method of electrostatic doping which allows us to reach a maximum n-doping density of 4 × 1014 cm−2 in few-layer MoS2 on glass substrates. With increasing carrier density we first induce an insulator to metal transition and subsequently an incomplete metal to superconductor transition in MoS2 with critical temperature ≈10 K. Contrary to earlier reports, after the onset of superconductivity, the superconducting transition temperature does not depend on the carrier density. Our doping method and the results we obtain in MoS2 for samples as thin as bilayers indicates the potential of this approach.

International audienceWe introduce a technique that we call Space Charge Doping for electrostatic doping of 2Dmaterials. This technique exploits the presence of mobile ionic species in glass to induce a chargeimbalance at the glass-material interface. Ionic mobility in glass is species dependent and also dependenton the temperature and the applied electric field. Mobility of positive sodium ions isincreased by heating and an applied electric field causes ion drift. The polarity of the electric fieldresults in accumulation or depletion of sodium ions at the glass surface inducing, respectively, electronor hole doping in the material placed on the surface, in this case graphene. Extremely highdoping levels are reached (>1014 cm2) without compromising graphene quality and with reversibility,bipolarity, and stability in tim