ASYMMETRICAL EFFECTS OF COPPER-SITE HOLES VERSUS OXYGEN-SITE HOLES IN LA-SR-CU-O

The effects of the copper-site holes and oxygen-site holes on structure, superconductivity, and normal state in La1.85Sr0.15CuO4 have been studied by use of a method in which the hole concentrations at both sites are varied independently. The filling of both the Cu2+ holes and the O- holes induces a tetragonal-to-orthorhombic structural transition. Such a behavior supports strongly the interpretation that the driving force for the bending of Cu-O-Cu bonds is the stabilization of the sigma-* antibonding interaction. The two hole-filling processes generate profoundly different effects on T(c), normal-state transport, and magnetic susceptibility. We will discuss the causes of these highly asymmetrical effects.