Pressure dependence of the carrier concentration in electron- and hole-doped Ln2CuO4 superconductors

Results of electronic structure calculations for the T-, T*-, and T'-phase superconductors show that the planar copper-apical oxygen bond length does not play a crucial role in determining the charge redistribution under pressure. The rare earth element, the contribution of which has been ignored upto now, plays a more important role. In all three structures we find that there is a small electron transfer from the CuO2 planes to the rare earth sites which act as electron reservoirs. This results in an increase in the carrier concentration in the CuO2 planes in the hole-doped superconductors and a decrease in the electron-doped superconductors. Assuming a direct relationship between Tc and the carrier concentration we obtain an increase in Tc in the hole-doped superconductors and a modest decrease in the electron-doped superconductors. (orig.)