Doping of Ce inT−La2CuO4: Rigorous test for electron-hole symmetry for high-Tcsuperconductivity

Abstract

We report that Ce doping was achieved in ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ with the ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}\phantom{\rule{0.3em}{0ex}}(T)$ structure for the first time by molecular beam epitaxy. A synthesis temperature of as low as $\ensuremath{\sim}$ $630\phantom{\rule{0.3em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and an appropriate substrate choice, $i.e.$, $(001){\mathrm{LaSrGaO}}_{4}\phantom{\rule{0.3em}{0ex}}({a}_{s}=3.843\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})$, enabled us to incorporate Ce into the ${\mathrm{K}}_{2}{\mathrm{NiF}}_{4}$ lattice and to obtain Ce-doped $T\text{\ensuremath{-}}{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ up to $x\ensuremath{\sim}0.06$. The doping of Ce makes $T\text{\ensuremath{-}}{\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ more insulating, which is in sharp contrast to Sr (or Ba) doping in $T\text{\ensuremath{-}}{\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$, which makes the compound metallic and superconducting. The observed smooth increase in resistivity from the hole-doped side $(T\text{\ensuremath{-}}{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4})$ to the electron-doped side $(T\text{\ensuremath{-}}{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4})$ indicates that the electron-hole symmetry is broken in the $T$-phase materials.