Electric field effect on insulating cuprate planes

Abstract

We have studied field effect doping of nearly insulating $p$-type ${\mathrm{CuO}}_{2}$ planes in single crystal transistor heterostructures. By using a high ${\ensuremath{\epsilon}}_{r}$ epitaxial ${\mathrm{SrTiO}}_{3}$ dielectric layer, a wide range of doping control is obtained, from $\ensuremath{-}0.40$ to 0.15 $\text{carriers}∕\mathrm{Cu}$ (or $\ensuremath{\sim}{10}^{14}\phantom{\rule{0.3em}{0ex}}\text{carriers}∕{\mathrm{cm}}^{2}$). While a considerable field effect is observed for carrier depletion, the induced holes are completely localized even up to carrier density levels far beyond the bulk insulator-to-superconductor transition value. This implies that large induced carrier density and single crystalline interface is not a sufficient condition for electric field induced insulator-to-superconductor transition for cuprates. We show that the induced carriers are almost confined to the top single ${\mathrm{CuO}}_{2}$ plane and propose that two-dimensional confinement introduces this localization. Understanding and overcoming this localization behavior is a serious challenge to any attempt to use electric field to induce superconductivity in insulating cuprates.