Theoretical Study On The Effect Of Non-magnetic Impurities Outside The CuO₂ On The Physical Properties Of Copper Oxide High Temperature Superconductors

The study of the effects of impurities in copper oxide materials is one of the hotspot issues to understand the mechanism of the high Tc materials. In this paper, within the t-J-U model and the Gutzwiller approximation, the effects on the local density of states of single impurity out of the CuCO2plane and many magnetic impurities in the plane in copper oxide materials are studied systemically using the BdG equation.The paper is organized as follows. In chapter ?, a brief review about the t-J-U model, the Gutzwiller approximation theory and the BdG equation is given. It is believed that the essential low-energy physics of copper oxide materials can be described effectively by the t-J-U model, while the electronic correlation is treated properly within the Gutzwiller approximation theory.In chapter ?, within t-J-U model we study the effect of single nonmagnetic impurity out of the CuO2plane in the copper oxide materials using the Gutzwiller approximation theory and BdG equation, especially the effect on the local density of state (LDOS). We find that away from the impurity, the LDOS shows typical "V" shape asmmetric curve. The superconducting gap reduces around the impurity, but the impurity does not destroy the superconducting. We find that the inhomogeneity originates from nonlinear screening of the ionic potential which introduced by the doped nonmagnetic impurity.In chapter IV, The local density of states(LDOS) around two nonmagnetic impurities which are located at different sites is studied within the two-dimensional t-J-U model. The order parameters are determined in a self-consistent way with the Gutzwiller projected mean-field approximation and the Bogoliubov-de Gennes theory. When the two impurities are located one or two sites away, we find the superconductivity coherence peaks are more strongly suppressed and the zero-energy peak(ZEP) has split into two peaks. Whereas when the two impurities are located next to each other, the ZEP vanished, and LDOS doesn't change a lot compared with the case away from the impurities.