  New advances in x-ray diffraction, extended x-ray absorption fine structure
EXAFS and x-ray absorption near edge structure XANES using synchrotron
radiation have now provided compelling evidence for a short range charge
density wave phase (CDW) called striped phase in the CuO2 plane of all cuprate
high temperature superconductors. The CDW is associated with a bond order wave
(BOW) and an orbital density wave (ODW) forming nanoscale puddles which coexist
with superconducting puddles below Tc. The electronic CDW crystalline phase
occurs around the hole doping 0.125 between the Mott charge transfer insulator,
and the 2D metal. The Van der Waals (VdW) theoretical model for a liquid of
anisotropic extended objects proposed for supercooled water is used to describe
: a) the underdoped regime as a first spinodal regime of a slightly doped
charge transfer Mott insulator puddles coexisting with the striped polaronic
CDW puddles; and b) the optimum doping regime as a second spinodal regime where
striped polaronic CDW puddles coexist with the normal 2D metal puddles. This
complex phase separation with 3 competing phases depends on the strength of the
anisotropic electron-phonon interaction that favors the formation striped
polaronic CDW phase.
