Two-Component Theory and Dynamic Structural Correlations

Abstract

In two-component theory1,2 pairing arises from localized negative-U states and mobility arises from extended single particle states. Signatures of this theory range from distinctive superconductive TC, Δ, HC, ζ to linear T dependence of the normal state resistance, and linear voltage dependent normal state tunneling conductance. A unique signature is the prediction of structural correlations which are local above TC and extended below TC. Experiments provide direct evidence for such dynamical correlations: neutron diffraction “thermal ovals”,2 channeling experiment cross section changes as a function of temperature near TC,3,4 pair-distribution-function neutron diffraction including inelastic and elastic scattering showing direct evidence for dynamic correlations which change at TC,5 and EXAFS showing oxygen atom tunneling between sites separated by 0.13 A.6 In two-component theory the implied strong lattice coupling is consistent with a low isotope shift since the tunneling occurs by a virtual Franck-Condon transition.