Spin and Charge Pairing Instabilities in Nanoclusters and Nanomaterials

Abstract

Our exact studies are focused on the understanding of pairing and magnetism arising from local electron correlations in tunneling probe responses in nanoclusters, assembled clusters of various geometries, nano and heterostructured materials, atomic scale experiments in inhomogeneous high T c cuprates, manganites, and other concentrated transition metal oxides. Interpretation of many body physics and local density states anomalies in scanning tunneling spectroscopy is given for electron charge and spin pairing instabilities in real space. Near crossing degeneracies or quantum critical points the electron configurations of the lowest energy levels control the low temperature physics of spontaneous transitions, phase separation, spatial inhomogeneities, and pairing that can be the important steps in deciphering the mystery of high T c superconductivity. The thermodynamic phase diagrams, obtained from exact canonical and grand canonical ensemble calculations in small clusters resemble a number of inhomogeneities, coherent and incoherent, paired and unpaired nanoscale phases found recently in Nb and Co nanoparticles, ultracold fermionic atoms, doped high T c cuprates, spin-charge separation in manganites, and multiferroic nanomaterials probed by scanning tunneling microscopy. We review experimental and theoretical descriptions of electron instabilities and intrinsic inhomogeneities in an ensemble of clusters, ultrasmall nanoparticles, and eventually bulk nanomaterials, which require modifications of the standard theories to implement the local electron correlations in the local building block structure to exhibit energy level discreteness and spatial inhomogeneities in novel nonstoichiometric nanomaterials.