Thermodynamic Properties Of Electron-doped Cuprate Superconductors

The mechanism of high temperature superconductors is still one of the most challenging problems in condensed matter physics. It is well known that electron-doped high-T_c materials have very different properties compared to hole-doped ones. Intensive study has been done on the superconducting and normal state properties of electron-doped high- T_c superconductors inthe past few years, with some consensus having been reached. However, several aspects are still controversial. For instance, the crossover of superconducting and antiferromagnetic regions in the phase diagram is under debate. In this paper, chemical potential, entropy and specific heat of electron-doped cuprate superconductors in the antiferromagnetic state, described by the t-t'-t" - J model, are calculated using the slave boson mean field approach. This paper is organized as follows. In chapter 1, the progress in the study of high- 7oxide superconductivity and several relevant theories are presented. In chapter 2, the properties of the electron-doped cuprate superconductors are described. In chapter 3, t-t'-t"-J model of strong correlation systems is introduced. In chapter 4, the slave boson mean field approach is established. In chapter 5, chemical potential, entropy and specific heat of electron-doped cuprate superconductors in the antiferromagnetie state, described by the t-t'-t"- J model, are calculated using the slave boson mean field approach. From the results attained for the chemical potential, it is found that the chemical potential is proportional to the doping level in a certain doping range and that the chemical potential depends on temperature quadratically. The entropy decreases as temperature increases. However, it is suppressed in the antiferromagnetie state. The electronic specific heat depends on temperature quadratically at low temperatures. It is found that the specific heat displays two distinct peaks, a low-temperature peak related to the spin degrees of freedom and high-temperature broad peak related to the charge degrees of freedom. It is found that the charge peak moves to a lower temperature with decreasing of the peak value and that the spin peak moves to a high temperature with decreasing of the peak value as the doping increases.