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

The metallic phase in doped cuprate perovskites is determined by both the hole doping delta and the micro-strain epsilon of the planar Cu-O bond length. The micro-strain epsilon in the CuO2 plane has been measured by Cu K-edge EXAFS and x-ray diffraction using synchrotron radiation. The critical micro-strain epsilon (c) for the onset of local lattice distortions (LLD) and stripe formation has been determined. The strain quantum critical point (QCP) is found at (epsilon (c)delta (c)). The superconducting critical temperature is measured as a function of two variables T-c(epsilon,delta) and it reaches its maximum at the strain QCP. The superconducting phase occurs in the region of critical fluctuations around this QCP. The critical fluctuations near the strain QCP drives the self-organization of the metallic plane forming a particular superlattice of quantum stripes called "superstripes" that favors the amplification of the superconducting critical temperature.