Theoretical Study Of Non-magnetic Impurities On The Physical Properties Of Copper Oxide High-temperature Superconductors

The study of the effects of nonmagnetic 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 and many nonmagnetic impurities in copper oxide materials are studied systemically using the BdG equation.The paper is organized as follows. In chapter II, 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 III, within t-J-U model and Gutzwiller approximation theory, we study the effect of single nonmagnetic impurity in the copper oxide materials using the BdG equation, especially the effect on the local density of state (LDOS). We find that with the increasing of the doping and the strength of the impurity, the impurity have a great effect on both the LDOS and the electron distribution:around the nonmagnetic impurity, a zero-energy peak is induced by the impurity, at the same time the superconducting coherence peaks are strongly suppressed by the impurity. And the intensity of the zero-energy peak increases with the increasing of the doping. Far away from the impurity, both the LDOS and the electron distribution show the same results as the uniform system.In chapter IV, using the BdG equation, we discuss the effects of many nonmagnetic impurities on the LDOS and the related physics properties within t-J-U model and Gutzwiller approximation. Our results show that for the situation of three and four impurities, the range of the effect of impurities is enlarged. For the situation of five impurities which distribute symmetrically:for I type impurities which distribute closely show that around the impurities, the intensity of the zero-energy peak is extremely high, at the same time the superconducting coherence peaks are strongly suppressed; for II type impurities which distribute dispersedly show that only local effect around each impurity which is familiar with the single nonmagnetic impurity case.