Displacement of Apical Oxygen of the Oxide Superconductors below T_c

Abstract

Pressure dependence of the transition temperature of the high-T_c Cu-oxide superconductors strongly suggests the importance of the apical oxygen. By an assumption that the distance between the CuO₂ plane and the apical oxygen governs the transition temperature, displacement of the apical oxygen below T_c is verified through the phenomenological Ginzburg-Landau theory. The magnitude of the displacement is estimated, and compared with various experiments.