Normal State Of Copper Oxide High-temperature Superconducting Materials Abnormal Physical Nature Of The Study

The study of the anomalous normal-state behaviors is the central problem in copper oxide materials. In this paper, within the t-J model and fermion-spin theory, the anomalous charge dynamics, spin dynamics and electron spectral function of copper oxide materials are studied systemically.The paper is organized as follows. In chapter II, a brief review about the t-J model and the fermion-spin theory is given. It is believed that the essential low-energy physics of copper oxide materials can be described effectively by the t-J model, while the local single occupancy constraint is treated properly within the fermion-spin theory. Within t-J model and fermion-spin theory, we study the anomalous charge dynamics in chapter III: firstly, we study the in-plane charge dynamics in the underdoped regime, and the influence of the additional second-neighbor hopping t' on the charge dynamics of the t-J model. We find that for the small values of t', the qualitative feature of the charge dynamics in the t-t'-J model is the same as in the case of the t-J model, where the conductivity spectrum shows the low-energy non-Drude peak and unusual midinfrared band, while resistivity exhibits a nearly temperature linear dependence with deviation at low temperature in the underdoped regime. Moreover, the additional second neighbor hopping t' leads to a clear shift of the position of the midinfrared band to the higher energies in the conductivity spectrum, and suppresses the range of the deviation from the temperature linear dependence in the resistivity. Furthermore, the c-axis charge dynamics of copper oxide materials in the underdoped and optimally doped regimes has been studied by considering the incoherent interlayer hop-ping. It is shown that the c-axis charge dynamics for the chain copper oxide materials is mainly governed by the scattering from the in-plane fluctuation, while the c-axis charge dynamics for the no-chain copper oxide materials is dominated by the scattering from the in-plane fluctuation incorporating with the interlayer disorder, which would be suppressed when the holon pseudogap opens at low temperatures and lower doping levels, leading to the crossovers to the insulating range in the c-axis resistivity and the temperature linear to the nonlinear range in the in-plane resistivity. Finally, the charge dynamics of the underdoped bilayer copper oxide materials is studied by considering the bilayer interactions, our results show that the qualitative behavior of the transport of the bilayer copper oxide materials is the same as in the single-layer case.In chapter IV we discuss the anomalous spin dynamics. Firstly, the incommensurate magnetic scatterring of the underdoped single-layer copper oxide materials in the normal state is studied. It is shown that away from the half-filling the commensurate peak is replaced by incommensurate peaks at [(1 ± 6)n, tt], [tt, (1 ± 5)n], and the incommensurability parameter S increases linearly with doping at the beginning and then saturates at higher dopings. These peaks broaden and weaken in amplitude with increasing energy. In particular, we predict a rotation of these peaks by tt/4 at even higher temperatures, being shifted to [(1 ± 5/y/2)n, (1 ± S/y/2)n]. Secondly, we discuss the influence of the additional second neighbor hopping if on the spin response of the t-J model, and find that for small values oft', although the additional second neighbor hopping if is systematically accompanied with the reduction of the dynamical spin structure factor and susceptibility, the integrated dynamical spin structure factor spectrum is almost if independent, and the integrateddynamical spin susceptibility still shows the particularly universal behavior as I(oj,T) oc arctan[aicu/T + a3(cu/T)3]. Furthermore, the doping and energy dependence of the spin dynamics of the underdoped bilayer copper oxide materials in the normal state is studied by considering the bilayer interactions, our results show that there are some similar behaviors between the single-layer and bilayer copper oxide materials at relatively low energy: the incommensurability parameter S increases linearly with doping at low dopings and then saturates at higher dopings, and the integrated dynamical spin susceptibility still shows the particularly universal behavior as in single-layer case. But for bilayer copper oxide materials, 5 is reduced with increasing energy, and the incommensurate peaks are converged to the commensurate resonance at the higher energy.In chapter V, the momentum and doping dependence of the electron spectral function and electron dispersion for copper oxide materials in the underdoped regime are studied. It is shown that the electron spectrum is changed with dopings, and the electron dispersion exhibits a flat band around (tt,O) point in the Brillouin zone, which leads to the normal-state pseudogap formation.