Electric field effect and superconducting–insulating transition in ‘123’ cupratesuperconductors

Abstract

The physics of high critical temperature superconductors (HTS) remains a fascinating butundisclosed issue in condensed matter. One of the most interesting topics is thetransition from the insulating phase of the parent compound, having long rangeantiferromagnetic order, to the superconducting phase. A method to investigate in detailthe superconducting to insulating (SIT) transition in HTS is to control the doping of theCuO2 planes in a fine way. Here, by using the electric field effect on thinNd1Ba2Cu3O7 films, we present a study of the HTS phase diagram close to the SIT with unprecedenteddetail. By virtue of these data, we will show that doping of holes in samples located at theboundary separating the superconducting and insulating regions produces changes in thetransport characteristic consistent with an electronic phase separation scenario. Someconsequences of these data are the failure of standard 2D quantum scaling theory and thepossible coexistence of superconducting and weakly insulating phases in this region of thephase diagram. A continuous transition between the two competing phases as afunction of doping place evident constraints on the mechanism of superconductivity.