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.
Categories: cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el