The strain quantum critical point for superstripes in the phase diagram ofall cuprate perovskites

The metallic phase in doped cuprate perovskites is determined by both the h ole doping delta and the micro-strain epsilon of the planar Cu-O bond lengt h. The micro-strain epsilon in the CuO2 plane has been measured by Cu K-edg e EXAFS and x-ray diffraction using synchrotron radiation. The critical mic ro-strain epsilon (c) for the onset of local lattice distortions (LLD) and stripe formation has been determined. The strain quantum critical point (QC P) is found at (epsilon (c)delta (c)). The superconducting critical tempera ture is measured as a function of two variables T-c(epsilon,delta) and it r eaches its maximum at the strain QCP. The superconducting phase occurs in t he region of critical fluctuations around this QCP. The critical fluctuatio ns near the strain QCP drives the self-organization of the metallic plane f orming a particular superlattice of quantum stripes called "superstripes" t hat favors the amplification of the superconducting critical temperature.