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

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 $\sim 2.8$ $\times$ 10${}^{21}$ cm${}^{-3}$ at room temperature (\emph{T}) at the optimally reduced condition. The in-plane resistivity ($\ddot{I}$${}_{ab}$) of the $n$-type samples exhibits a quadratic \emph{T} dependence in the moderate-\emph{T} range and shows an anomaly at a relatively higher \emph{T} probably related to pseudogap formation analogous to underdoped Nd${}_{2-x}$Ce${}_x$CuO${}_4$ (NCCO). Furthermore, $\ddot{I}$${}_{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.

4 pages, 5 figures