Pressure effect on T-c for the rare-earth series RBa2Cu3O7-delta

The pressure dependence of the superconducting transition temperature T-c i n RBa2Cu3O7-delta (R=Y and rare earths) series has been investigated system atically on the basis of the t-t'-t "-J model with d-wave pairing by taking into account the variations of the hole concentration in the CuO2 planes a nd the effective interaction with pressure. It is shown that the pressure i nduced change of hole concentration increases with the trivalent rare-earth ion radius. The calculated T-c and its pressure derivative dT(c)/dP are fo und to be the increasing functions of the radius of the R3+ ions for the fu lly oxygenated RBa2Cu3O7. Good agreement with experiments suggests that the rare-earth ion size effect on dT(c)/dP in RBa2Cu3O7 mainly originates from the pressure-induced charge transfer from the charge reservoir CuO chain t o the conducting CuO2 planes. The change of dT(c)/dP with hole concentratio n and the pressure dependence of T-c in the recently discovered superconduc ting PrBa2Cu3Oy are well reproduced in this simple model. We have arrived a t the conclusion that the unusually large T-c enhancement in PrBa2Cu3O7 und er pressure results from its underdoped nature. Further experiments are pro posed to enhance T-c at ambient pressure in PrBa2Cu3Oy.