Enhancement of superconducting transition temperature in electrochemically etched FeSe/LaAlO3 films

We investigated the gate voltage dependence of Tc in electrochemically etched FeSe films with an electric-double layer transistor structure. The Tczero value of the etched FeSe films with a lower gate voltage (Vg = 2.5 and 3.3 V) reaches 46 K, which is the highest value among almost all reported values from the resistivity measurements except for the data by Ge et al. This enhanced Tc remains unchanged even after the discharge process. Our results suggest that the origin of the increase in Tc is not electrostatic doping but rather the electrochemical reaction at the surface of an etched films.