Theoretical research will be conducted on two general areas of modern condensed matter physics: the electronic structure of correlated electron systems and the nature of the superconductor- insulator transition in the cuprate superconductors. In the first area, studies will be performed on the influence of oxygen-hole copper-hole pairing on the d-wave superconductivity in the cuprates. As temperature is lowered below the transition temperature there is the possibility of a second phase transition signaling the onset of copper-oxygen pairing. Also to be studied is the nature of the electron pairing in potassium fulleride and the possibility of a special, Berry phase, electron-phonon interaction in the fullerenes. In the second area, studies will be performed on the possibility that the superconductor-insulator transition which occurs with zinc doping in the cuprates represents a simultaneous localization of Cooper pairs and partial de-pairing induced by disorder and/or magnetic fluctuations. In a related but separate study, the effects of incipient boson localization on the quantum tunneling of vortices when the system is close to a field-induced superconductor-insulator transition will be investigated. %%% Theoretical research will be conducted on fundamental problems in condensed matter physics which can have a major impact on understanding the behavior of the high temperature superconductors. The research will primarily focus on the copper-oxide based superconductors. Work will be done on the nature of the transition as the material goes from a superconducting state to an insulating state.
