Ce doping in T-La2CuO4 films: Broken electron-hole symmetry for high-Tc superconductivity

We attempted Ce doping in La2CuO4 with the K2NiF4 (T) structure by molecular beam epitaxy. At low growth temperature and with an appropriate substrate choice, we found that Ce can be incorporated into the K2NiF4 lattice up to x ∼ 0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes T-La2−xCexCuO4 more insulating, which is in sharp contrast to Ce doping in La2CuO4 with the Nd2CuO4 structure, which makes the compounds superconducting. The observed smooth increase in resistivity from hole-doped side (T-La2−xSrxCuO4) to electron-doped side (T-La2−xCexCuO4) indicates that electron-hole symmetry is broken in the T-phase materials.