Indications of an Electronic Phase Transition in Two-Dimensional Superconducting ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ Thin Films Induced by Electrostatic Doping

Indications of an Electronic Phase Transition in Two-Dimensional Superconducting ${YBa}_{2} {Cu}_{3} O_{7 - x}$ Thin Films Induced by Electrostatic Doping

Xiang Leng, Javier Garcia-Barriocanal, Boyi Yang, Yeonbae Lee, J. Kinney, and A. M. Goldman

Phys. Rev. Lett. 108, 067004 – Published 10 February 2012

Abstract

We successfully tuned an underdoped ultrathin ${YBa}_{2} {Cu}_{3} O_{7 - x}$ film into the overdoped regime by means of electrostatic doping using an ionic liquid as a dielectric material. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and a different two-step doping mechanism for electrostatic doping was revealed. The normal resistance increased with carrier concentration on the overdoped side and the high temperature (180 K) Hall number peaked at a doping level of $p \sim 0.15$ . These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.