Metallic state in La-doped YBa$_2$Cu$_3$O$_y$ thin films with $n$-type charge carriers

TL;DR

This study demonstrates the successful synthesis of La-doped YBa₂Cu₃O_y thin films exhibiting both hole and electron doping, revealing metallic behavior and pseudogap features, and highlighting asymmetry and potential for ambipolar superconductivity.

Contribution

It reports the first observation of n-type metallic behavior in La-doped YBCO thin films with detailed transport properties and pseudogap features, expanding the understanding of doping asymmetry in cuprates.

Findings

n-type YBCO films show metallic behavior with high carrier density

Resistivity exhibits quadratic temperature dependence and pseudogap-like anomalies

Evidence of electron-hole asymmetry and potential for ambipolar superconductivity

Abstract

We report hole and electron doping in La-doped YBa$_2$Cu$_3$O$_y$(YBCO) thin films synthesized by pulsed laser deposition technique and subsequent \emph{in-situ} postannealing in oxygen ambient and vaccum. The $n$-type samples show a metallic behavior below the Mott limit and a high carrier density of $\sim2.8$ $\times$ 10$^{21}$ cm$^{-3}$ at room temperature (\emph{T}) at the optimally reduced condition. The in-plane resistivity ($\rho$$_{ab}$) of the $n$-type samples exhibits a quadratic \emph{T} dependence in the moderate-\emph{T} range and shows an anomaly at a relatively higher \emph{T} probably related to pseudogap formation analogous to underdoped Nd$_{2-x}$Ce$_x$CuO$_4$ (NCCO). Furthermore, $\rho$$_{ab}$(T), \emph{T}$_c$ and \emph{T} with minimum resistivity (\emph{T}$_{min}$) were investigated in both $p$- and $n$-side. The present results reveal the $n$-$p$ asymmetry (symmetry) within the metallic-state region in an underdoped cuprate and suggest the potential toward ambipolar superconductivity in a single YBCO system.