Modulation of Superconductor-Insulator Transition in NdBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-x\thinspace }}$through Oxygen Migration by Electrolyte Gating

The technique of electric double layer transistor (EDLT) has been applied to several HTS, such as LSCO and YBCO. The interpretation of SIT in all these studies are attributed to electrostatically induced carriers. However, in several electrolyte gating experiments recently, the effect is mainly attributed to oxygen vacancy formation, with migration of oxygen from the film into ionic liquid. In this study, the modulation of SIT is performed in a 7uc NBCO EDLT. By applying positive V$_{\mathrm{g}}$, the SC NBCO gradually transits to insulating. When V$_{\mathrm{g}}$ changes back to 0V, it remains insulating. If the mechanism is electrostatically induced carriers, it should recover SC. However, it is only when applying a reverse negative V$_{\mathrm{g}}$ that it can gradually recover SC. Meanwhile, after SIT and V$_{\mathrm{g}}$ back to 0V, another sample is taken out from PPMS. After careful remove of ionic liquid, it remains insulating. After annealing at O$_{\mathrm{2}}$ atmosphere, it recovers SC. These strongly support the underlying mechanism is oxygen migration, instead of electrostatically induced carriers. The R$_{\mathrm{c}}$ is extracted to be about 5320$\Omega $, suggestive of quantum phase fluctuation.