RELATIONSHIP BETWEEN PRESSURE-INDUCED CHARGE-TRANSFER AND THE SUPERCONDUCTING TRANSITION-TEMPERATURE IN YBA2CU3O7-DELTA SUPERCONDUCTORS

A model is proposed for the pressure dependence of Tc based on the inverted parabolic relationship between Tc and the hole carrier density n that takes into account the fact that Tc drops to zero for a minimum value nmin or a maximum value nmax of n. The models proposed previously by Almasan et al. and Neumeier and Zimmermann are recovered, and are shown to be quite similar. Detailed calculations for YBa2Cu3O7-δ superconductors show that one can obtain large enhancements in Tc under pressure in materials that are highly underdoped, or have relatively modest rates of pressure-induced charge transfers. On the other hand, Tc enhancements in compounds which are near optimum doping or which have large rates of pressure-induced charge transfers are found to be quite modest. © 1995 The American Physical Society.