The Study Of The X-ray Photoemission Spectroscopy On The Electron Doped Superconductor Nd_2-xCe_xCuO₄

In the case of electron-doped cuprates high-temperature superconductors RE2-xCexCuO4±δ(RE=Nd, Sm, Pr, La), doping alone by substituting the trivalent ions RE3+ with tetravalent Ce4+ is insufficient, and annealing the as-grown sample in low-oxygen environment to remove a tiny amount of oxygen is necessary to induce superconductivity. For this nature, physicists have done a lot of relevant theoretical and experimental studies to explain that. However, the role of oxygen reduction process leading to superconductivity remains a persistent controversial issue.In this paper, we have researched X-ray photoemission spectra of Nd1.85Ce0.15CuO4-δsingle crystal under different annealing conditions, and proposed that annealing process could remove excess oxygens and make the conductive electrons delocalized to induce superconductivity. This article also publishes a utility model patent "a thermopower measurement system" of The People's Republic of China State Intellectual Property Office, which describes the technical details of the thermopower measurement in detail.In chapter 1, we review the history of high-temperature superconductors, then describe the crystal structure of the copper oxide high-temperature superconductors, phase diagram, thermopower and the theory of annealing process. Finally, we summarize some of the superconducting theory of the copper oxide high-temperature superconductors.In chapter 2, we review the history of photoemission study about the copper oxide high-temperature superconductors copper oxides. One explains the cluster model that is equivalent to copper oxide, and cites a number of research results on Bi2212, Y123, and R2-xCexCuO4. Finally, we introduce some of the new technologies about photoelectron spectroscopy.In chapter 3, We have studied the Cu 2p, Nd 3d and valence band X-ray photoemission spectra obtained for Nd1.85Ce0.15CuO4-δsingle crystal under different annealing conditions. It is found that both the 2p3/23d10 and 2p1/23d10 peaks of Cu 2p core level appear obviously after oxygen reduction. Nd 3d spectra move towards lower binding energy after reduction. Finally, the changes of the ratio of IM/IS and the density of states near the Fermi level are shown in the valence spectra.,and we also find that clear Fermi edges is formed after annealing for 24 hours. All the changes of the Cu 2p, Nd 3d and valence band spectra can be explained in terms of the delocalization of itinerant electrons. We suggest annealing process could remove excess oxygens and the associated disordered potential to make the conductive electrons delocalized so that superconductivity becomes possible. In chapter 4, we disclose a utility patent about a thermopower measurement system. This system includes temperature measurement and thermopower measurement devices, data processing equipment and temperature control devices. Among them, the temperature measurement and thermoelectric power measuring devices further include noise filtering devices, thermometers, etc., which are connected with the data processing devices through the GPIB bus, data processing devices are connected to the temperature control devices through the digital - analog conversion card, temperature control devices further include the heater, the voltage signal amplification devices and current signal amplification devices. This system could provide shorter measurement time. Its temperature is quasi-continuous, and it can directly measure the impact of different temperature changing rates on thermopower materials.