Ionic gating in the study of superconductivity

Abstract

The tuning of the carrier density is pivotal for uncovering the underlying superconducting mechanisms and constructing quantum devices because the carrier density is a major parameter that influences superconductivity. However, the carrier density is frequently entangled with other physical degrees of freedom. Tuning the carriers via chemical doping will perturb the pristine crystal lattice, thereby making independent control of carrier density difficult to realize. In the recent development on ionic gating, the advantages of traditional chemical doping and field-effect tuning have been combined, i.e., in situ and reversible tuning of the carriers in a large amount is achieved. In the recent rapid advances of ionic gating, two complementary schemes, i.e., electrostatic field-effect tuning and electrochemical doping, have been coherently developed. This review summarizes the application of ionic gating in inducing novel superconductivity and tuning the properties of high-temperature superconductors. Electrostatic field-effect tuning using ionic liquids can induce superconductivity in insulating/semiconducting systems with excellent efficiency, whereas electrochemical doping plays an essential role in tuning metallic samples with intrinsically high carrier densities. Thus, because of the unparalleled tuning capability and the ease of incorporation of ionic gating with other characterization techniques, it is expected to become an indispensable technique for investigating superconductivity, based on which unexplored phase diagrams with high precision can be obtained, and contribute to the comprehension of novel superconducting states such as the high-temperature superconductivity.