Doping of Ce in T-La2CuO4: Rigorous test for electron-hole symmetry for high-Tc superconductivity

We report that Ce doping was achieved in La2CuO4 with the K2NiF4 (T) structure for the first time by molecular beam epitaxy. A synthesis temperature of as low as ~ 630C and an appropriate substrate choice, i.e., (001)LaSrGaO4 (a \~ 3.843 A), enebled us to incorporate Ce into K2NiF4 lattice and to obtain Ce-doped T-La2-xCexCuO4 up to x ~ 0.06. The doping of Ce makes T-La2CuO4 more insulating, which is in sharp contrast to Sr (or Ba) doping in T-La2CuO4, which make the compound metallic and superconducting. The observed smooth increase in resistivity from the hole-doped side (T-La2-xSrxCuO4) to the electron-doped side (T-La2-xCexCuO4) indicates that the electron-hole symmetry is broken in the T-phase materials.