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

Abstract

We attempted Ce doping in La 2 CuO 4 with the K 2 NiF 4 (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 K 2 NiF 4 lattice up to x ~ 0.06, which had not yet been realized in bulk synthesis. The doping of Ce makes T-La 2-x Ce x CuO 4 more insulating, which is in sharp contrast to Ce doping in La 2 CuO 4 with the Nd 2 CuO 4 structure, which makes the compounds superconducting. The observed smooth increase in resistivity from hole-doped side (T-La 2-x Sr x CuO 4 ) to electron-doped side (T-La 2-x Ce x CuO 4 ) indicates that electron-hole symmetry is broken in the T-phase materials.

Valence of Ce in T- and T′-La2−xCexCuO4

“…We have recently succeeded in substituting Ce at the La site in T-La 2 CuO 4 by a molecular beam epitaxy (T represents the K 2 NiF 4 structure) [5,6]. However, the resultant TLa 2Àx Ce x CuO 4 was insulating up to x = 0.06.…”