Evidence for the strain critical point in high Tc superconductors

We report experimental evidence fur the phase diagram of doped cuprate superconductors as a function of the micro-strain epsilon of the planar Cu-O bund length, measured by Cu K-edge EXAFS, and hole doping delta. The local lattice distortions are measured by EXAFS and the charge ordering is measured by synchrotron radiation diffuse X-ray diffraction. This phase diagram shows a QCP at P(epsilon (c)delta (c)) where for epsilon > epsilon (c) charge-orbital-spin stripes and free carriers co-exist. The superconducting phase occurs in the region of critical fluctuations around this QCP. Thr function T(c) (epsilon, delta) of two variables shows its maximum at the strain QCP. The critical fluctuations near tills strain QCP give the self-organization of a metallic superlattice of quantum wires "superstripes" that favors the amplification of the critical temperature.