Breakthrough in 201203/01/2013
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 because the continuous tuning of carriers is challenging for conventional chemistry. This difficulty could be overcome by using a combination of liquid and solid gating to achieve quasi-continuous electrostatic carrier doping. In an exemplary band insulator, MoS2, researchers in university of Tokyo and RIKEN revealed a large enhancement in the transition temperature (Tc) occurring at optimal doping in the chemically inaccessible low-carrier density regime. Comparing with superconductivity induced in the same material using alkali metal doping studied 30 years ago, the field-induced superconductivity merit a 40% increase of Tc. The dome-like superconducting phase of MoS2, together with earlier report similar superconducting phase in LaAlO3/SrTiO3 interface and KTaO3, indicate that the superconducting dome might be a universal feature in many doped band insulators.
The present observation of a dome-like phase diagram, an enhanced Tc, and the electrostatic method to induce them may also pave a promising path to novel electronic devices such as superconducting transistors by harvesting the relatively high Tc of 10 K in MoS2. The dome-like phase diagram might host field-controllable competing phase parameters rich for new electronic functionalities, which would certainly be an emerging unexplored paradigm for the future researches.
Phase diagram of superconductivity of electrostatically doped MoS2. The colored areas indicate different ground states that cover different carrier densities, n2D. Optimum doping appears at a carrier density of 12×1014 cm-2 in a dome like superconducting phase.
J. T. Ye, Y. J. Zhang, R. Akashi, M. S. Bahramy, R. Arita, and Y. Iwasa “Supercondcuting Dome in a Gate Tuned Band Insulator”, Science 338 1193 (2012).