PRESSURE-DEPENDENCE OF THE HOLE CONCENTRATION IN SUPERCONDUCTING LA1.85SR0.15CUO4

Results of electronic structure calculations for La1.85Sr0.15CuO4 are presented in order to understand the effect of pressure on the charge redistribution. Our calculations show that the effect of pressure on the charge redistribution are rather subtle. In particular, we find that, contrary to what has been believed, the planar copper-apical oxygen (Cu-O(2) bond length does not play an important role in determining the charge redistribution under pressure. The deciding role is in fact exercised by the La-O bond lengths. The apical oxygens essentially serve as a conduit for charge transfer from the CuO2 planes to the lanthanum sites under pressure. With the crystal structure data of both Pei et al. and Nelmes et al., which exhibit Cu-O(2) bond length variations in completely opposite directions with pressure, an increase in the hole concentration in the CuO2 plane is obtained. However, assuming a linear relationship between T(c) and the hole concentration, we recover the pressure dependence of T(c) observed experimentally with the data of Pei et al. while with the data of Nelmes et al. a somewhat higher dependence is obtained.