Doping Effects Of Electrons And Holes On Superconducting Cuprates

It is great significant to clarify whether the mechanism of superconductivity in hole-doped and electron-doped cuprate superconductors can be understood with a unified physical mechanism. For hole-doped La2-χSrχCuO4+δ(LSCO) and electron-doped Nd2-χCeχCu04-δ(NCCO), the value of Tcmax, the doping range of superconductivity and some details of phase diagram are quite different. Because hole-doped (LSCO) and electron-doped (NCCO) are obtained by doping in different materials, it is difficult to determine the different properties of hole-doped and electron-doped cuprate superconductors either come from different materials or intrinsic properties of different carries. It is not benefit to understand the mechanism of superconductivity. So, it is necessary to find a system which can be doped with both electrons and holes. The first work of my paper is to find such a system. Therefore, we propose a system of La1-χ/2Pr1-χ/2MxCuO4, which can be doped by both electrons(M=Ce) and holes(M=Sr). In this system, the effects of different matrix are weakened and the effects of electrons and holes carrier are dominant factor.In this paper, the second what we concern is that different characteristics caused by Cu-sites doping on hole-doped and electron-doped cuprate superconductors. The microstructure of the CuO2 planes plays a key role in high temperature superconductivity, the characteristics of CuO2 planes is essential to understand the superconductivity and the anomalous normal state behavior. Partly substitution for Cu site is effective method. For hole-doped and electron-doped superconductors, it is found that the doping effects of magnetic element and non-magnetic element are quite different. In order to explain the mechanism of this phenomenon deeply and considering the special magnetism of Mn, we have studied the doping effects of Mn in hole-doped superconductor, La1-χ/2Pr1-χ/2SrχCuO4 and electron-doped superconductor, Nd2-χCeχCu04, including the effects of Mn substitution for Cu on structure, magnetism of normal state and superconductivity.Although the Tc of cuprate superconductors depends on carrier concentration in CuO2 plane, there are many ways to introduce carriers, usually; concentration of carrier can be changed by chemical substation for rare earth site or by changing oxygen content. For electron-doped high-Tc superconductors RE2-χCeχCu04-δ(RE=La, Pr, Nd, Sm, Eu), the moderate adjustment of oxygen content is important method to get superconducting phase. In my paper, we can adjust oxygen content quantitatively by developing a new technique. It is benefit to understand the important role of oxygen content on superconductivity. We conclude that different methods of introducing carriers have different effects on superconductivity by comparing to La2-χCexCu04-ν.The systems that we have studied are PrLai1-χSrχCuO4, Pr1-χLaCeχCuO4, La1-χ/2Pr1-χ/2SrχCuO4,La1-x/2Pr1-x/2CeCxCu04,Nd1.85Ce0.15Cu1-χMnχ04,La0.925Pr0.925Sr0.15Cu1-χMnχ04,Pr1.85Ce0.15Cu04-χ,Pr2Cu04-x and Pr1.85Ce0.15Cui1-χFeχO3.9.The dissertation was arranged as five parts.In first chapter, we reviewed structure, phase diagram of high-Tc superconductors and anomalous normal state properties. The recent development of theories and experimental results about this topic is mentioned.In second chapter, Sr and Ce have been doped respectively into the same matrix PrLaCuO4.We find that the PrLa1-χSrχCuO4 (PLSCO) are hole-doped T-214 structure while Pr1-χLaCeχCuO4 (PLCCO) are T-214 structure. For PLSCO, superconductivity can be achieved when 0.05≤x≤0.30 and Tc reaches its maximum value at x=0.15,Tcmax=26K while PLCCO with a range of 0.08≤x≤0.15 and Tcmax=24.9K at x=0.12. Anti-ferromagnetic transition is observed in PLCCO with its Neel temperature TN=35K.In third chapter, we have studied the system of Lai1-χ/2Pr1-χ/2MχCuO4 (M can be Sr or Ce). The La1-χ/2Pr1-χ/2SrχCu04 (LPSCO) are hole-doped T-214 structure, while the La1-χ/2Pr1-χ/2CeχCuO4 (LPCCO) are T-214 structure. For LPSCO, Tc reaches its maximum value at x=0.18, TCmax=26K. A logarithmic contribution to resistivity has been observed in underdoped regime, and such a logarithmic component vanishes in the overdoped regime. For LPCCO, superconducting transition is observed in the range of 0.08