Abstract
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 MoSe2, MoTe2 and WS2 by ionic gating in different regimes. Electrostatic gating using ionic liquid was able to induce superconductivity in MoSe2 but not in MoTe2 because of inefficient electron accumulation limited by electronic band alignment. Alternative gating using KClO4/polyethylene glycol enabled a crossover from surface doping to bulk doping, which induced superconductivities in MoTe2 and WS2 electrochemically. These new varieties greatly enriched the TMD superconductor families and unveiled critical methodology to expand the capability of ionic gating to other materials.
Highlights
Semiconducting transition metal dichalcogenides (TMDs) have attracted considerable interest as typical two-dimensional (2D) materials
Due to their weak bonds formed through van der Waals interactions between the layers, thin flakes of MX2 can be readily isolated from bulk material via mechanical exfoliation and fabricated into field effect transistors (FETs) devices
We used the EDL transistors (EDLTs) structure and employed DEME-TFSI as a gate dielectric; the latter is a widely used ionic liquid (IL) that has been demonstrated to be capable of accumulating a high density of carriers at the interface even at low bias voltages[15]
Summary
Semiconducting transition metal dichalcogenides (TMDs) have attracted considerable interest as typical two-dimensional (2D) materials. Flat and chemically stable thin layers of TMDs can be readily obtained via graphene-like mechanical exfoliation[1] from bulk crystals due to the weak van der Waals interaction-based interlayer bonding[2] By virtue of their semiconducting nature and defect-free crystal surfaces, thin exfoliated TMD layers are regarded to be ideal channel materials for field-effect transistors (FETs)[3,4,5] and TMD-based FETs have been shown to possess remarkable electronic[6,7] and opto-valleytronic properties[8,9,10,11,12,13] as well as promising prospects for device applications[14]. This study established new strategies for ionic gating both for electrostatic charge accumulation and electrochemical carrier doping, thereby providing new capability for accessing a wide carrier concentration range and extending superconductivity in other material series
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