Dynamical Local Lattice Instability Triggered High Tc Superconductivity

High Tc cuprate superconductors are characterized by two robust features: their strong electronic correlations and their intrinsic dynamical local lattice instabilities. Focusing on exclusively that latter, we picture their parent state in form of a quantum vacuum representing an electronic magma in which bound diamagnetic spin-singlet pairs pop in and out of existence in a Fermi sea of itinerant electrons. The mechanism behind that resides in the structural incompatibility of two stereo-chemical configurations Cu II O4 and Cu III O4 which compose the CuO2 planes. It leads to spontaneously fluctuating Cu-O-Cu valence bonds which establish a local Feshbach resonance exchange coupling between bound and unbound electron pairs. The coupling, being the only free parameter in this scenario, the hole doping of the parent state is monitored by varying the total number of unpaired and paired electrons, in chemical equilibrium with each other. Upon lowering the temperature to below a certain T * , bound and unbound electron pairs lock together in a local quantum superposition, generating transient localized bound electron pairs and a concomitant opening of a pseudo-gap in the single-particle density of states. At low temperature, this pseudo-gap state transits via a first order hole doping induced phase transition into a superconducting state in which the localized transient bound electron pairs get spatially phase correlated. The mechanism driving that transition is a phase separation between two phases having different relative densities of bound and unbound electron pairs, which is reminiscent of the physics of 4 He-3 He mixtures. PACS numbers: I INTRODUCTION Quite independent on any microscopic mechanism leading to superconductivity, this phenomenon is generated by establishing a macroscopic coherent quantum state in which an ensemble of transient bosonic charge carriers (composed of diamagnetic electron-pairs), having arbitrary phases in the parent state above T c , undergoes a global spontaneous symmetry breaking (SSB). The arbitrary phases of these virtual bosonic entities are thereby locked together into a unique global (though arbitrary) phase, the excitations of which are symmetry restoring collective Goldstone modes. In a current carrying state their existence assures the persistence of the resistance-less conduction through the Anderson-Higgs mechanism, by which they contribute to set up a longitudinal component of the electromagnetic vector potential dr