Effect of planar elastic strain on cuprate superconductivity

Elastic strain has important effects on the properties of hole doped superconducting cuprates, most significantly on Tc. While c-axis compression primarily enhances the number of hole carriers n, the intrinsic Tcintr is determined by the in-plane lattice parameter a, or the area of the CuO2 planes A. For optimal doping, dTc/dn=0, the available high pressure data suggest Tc ∝A-2, universally within the various cuprate families. This significant relationship requires A(n) to exhibit an extremum around nopt=0.16, ubiquitously observed as ''bulging'' anomaly riding the monotonous contraction of A from increasing covalency. We propose to express these findings in terms of the magnetoelastic strain exerted on the CuO2 lattice by pseudo-gapped excitations of preformed 3a hole pairs with nn repulsion.