Tunable superconductivity and phase transitions by field effect transistor

Date(s) - Jul 24 2017
11:00 AM - 12:00 PM

Room 335, McCullough Building


Tunable superconductivity and phase transitions by field effect transistor

Xianhui Chen

Department of Physics, University of Science and Technology of China

Hefei, Anhui 230026, China


In the field effect transistor (FET), electric field is adopted to control physical performance via tuning the carrier density. Such controllability through an electrostatic doping greatly promotes the development of research and industry for semiconductors. However, conventional metal-insulator-semiconductor (MIS) FET can only sustain very limited carrier density, and cannot meet further demands, especially in exploring high temperature superconductivity.

Consequently, researchers attempt to seek for FET with new gate dielectric, such as the electric double layer FET (EDL-FET) based on liquid ions to break this bottleneck. In this talk, we report high temperature superconductivity with an onset above 40 K can be achieved in an FeSe thin flake with Tc less than 10 K by tuning carrier with this EDL-FET technique. We also report on a novel FET device using solid ion conductor (SIC) as a gate dielectric, developed by our group, to overcome the inherent drawbacks of both MIS- and EDL-FET devices. Based on this SIC-FET technique, we achieved an optimal Tc of 46.6 K in FeSe thin flakes. In contrast to the EDL-FET based on liquid ion dielectric, SIC-FET can tune carrier concentration in a wider range, so that the complete phase diagram of FeSe superconductor can be mapped out. An superconductivity- insulating state transition is observed. Two new structural phases of LixFe2Se2 are obtained due to the Li intercalation driven by electrical field. A discrete superconducting phase diagram is observed in LixFeSe system. We also study the phase diagram of FeSe0.5Te0.5 and Bi2Se3 using SIC-FET. It is found that the phase diagram of FeSe0.5Te0.5 is quite different from that of FeSe because substitution of Te for Se may leads to a change of nature of FeSe layer. We will show you the evolution of topological insulator to superconductor for Bi2Se3 by the gating with SIC-FET.