Equivalence of the strain and doping dependence of the superconductive Tc in LaSrCuO: influence of the metal-insulator transition

It has long been known that oxygen doping, cation doping and strain all strongly influence the superconducting transition temperature, T_c, of high temperature superconductors (HTS). These factors become especially important when thin films are prepared for electronic devices where sample uniformity and reproducibility are crucial. To date, there has been no detailed understanding of the comparative roles that each parameter plays in determining T_c and thus predicting what T_c will result from a particular process is problematic. We have shown that the very different strain and doping dependencies in the prototypical HTS material, LSCO, can be reduced to a common dependence upon the conductivity. The shape of the common phase boundary is related to the metal-insulator transition in accordance with that recently discovered for many other superconducting systems. The implication for this and other high T_c systems is that only one, easily measured parameter, conductivity, need be determined or controlled.