Superconducting Dome in a Gate-Tuned Band Insulator

What Do You Know? A Dome The superconducting dome—the appearance of a maximum in the transition temperature as a function of a tuning parameter—has been observed in compounds such as cuprates, pnictides, and heavy fermion materials and is thought of as a signature of unconventional superconductivity. Ye et al. (p. 1193) used a liquid gating technique combined with back gating to finely tune the carrier density in the band insulator MoS2, which allowed them to observe the formation of a dome. The unexpected finding awaits theoretical explanation but may suggest that the appearance of an optimal carrier density may be a more common occurrence than was previously thought. Liquid gating tunes the carrier density in molybdenum disulfide, revealing unconventional superconductivity. A dome-shaped superconducting region appears in the phase diagrams of many unconventional superconductors. In doped band insulators, however, reaching optimal superconductivity by the fine-tuning of carriers has seldom been seen. We report the observation of a superconducting dome in the temperature–carrier density phase diagram of MoS2, an archetypal band insulator. By quasi-continuous electrostatic carrier doping achieved through a combination of liquid and solid gating, we revealed a large enhancement in the transition temperature Tc occurring at optimal doping in the chemically inaccessible low–carrier density regime. This observation indicates that the superconducting dome may arise even in doped band insulators.

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