Abstract:
The Fermi surface calculated within the rotating antiferromagnetism theory undergoes a topological change when doping changes from p-type to n-type, in qualitative agreement with experimental data for n-type cuprate Nd2？xCexCuO4 and p-type La2？xSrxCuO4. Also, the reconstruction of the Fermi surface, observed experimentally close to optimal doping in p-type cuprates, and slightly higher than optimal doping in the overdoped regime for this n-type high-TC cuprate, is well accounted for in this theory. This reconstruction is a consequence of the quantum criticality caused by the disappearance of rotating antiferromagnetism. The present results are in qualitative agreement with recently observed quantum oscillations in some high-TC cuprates. This paper presents new results about the application of the rotating antiferromagnetism theory to the study of the electronic structure for n-type materials.

Abstract:
Using variational cluster perturbation theory we study the competition between d-wave superconductivity (dSC) and antiferromagnetism (AF) in the the t-t'-t''-U Hubbard model. Large scale computer calculations reproduce the overall ground state phase diagram of the high-temperature superconductors as well as the one-particle excitation spectra for both hole- and electron-doping. We identify clear signatures of the Mott gap as well as of AF and of dSC that should be observable in photoemission experiments.

Abstract:
The magnetic response expected from a state characterized by rotating antiferromagnetism in a neutron-scattering experiment is calculated. We predict the occurrence of a peak at the frequency of the rotation of the rotating antiferromagnetic order parameter. The doping dependence of this frequency is very similar to that of the frequency of the magnetic resonance observed in the neutron-scattering experiments for the hole-doped high-$T_C$ cuprates. This leads us to propose the rotating antiferromagnetism as a possible mechanism for this magnetic resonance. We conclude that while the magnitude of the rotating antiferromagnetic order parameter was previously proposed to be responsible for the pseudogap and the unusual thermodynamic and transport properties, the phase of the rotating order parameter is proposed here to be responsible for the unusual magnetic properties of the high-$T_C$ copper-oxide superconductors.

Abstract:
The quantum interference effects due to the Aharonov-Bohm-type phase factors are studied in the layered $t-t'-t_\perp-U-J$ strongly correlated system relevant for cuprates. Casting Coulomb interaction in terms of composite-fermions via the flux attachment facility, we argue that U(1) compact group instanton events labeled by a topological winding number are essential configurations of the phase field dual to the charge. The impact of these topological excitations is calculated for the phase diagram, which displays the "hidden" quantum critical point.

Abstract:
We calculated the self-energy corrections beyond the mean-field solution of the rotating antiferromagnetism theory using the functional integral approach. The frequency dependence of the scattering rate ${1}/{\tau}$ is evaluated for different temperatures and doping levels, and is compared with other approaches and with experiment. The general trends we found are fairly consistent with the extended Drude analysis of the optical conductivity, and with the nearly antiferromagnetic Fermi liquid as far as the ${\bf k}$-anisotropy is concerned and some aspects of the Marginal-Fermi liquid behavior. The present approach provides the justification from the microscopic point of view for the phenomenology of the marginal Fermi liquid ansatz, which was used in the calculation of several physical properties of the high-$T_C$ cuprates within the rotating antiferromagnetism theory. In addition, the expression of self-energy we calculated takes into account the two hot issues of the high-$T_C$ cuprate superconductors, namely the Fermi surface reconstruction and the hidden symmetry, which we believe are related to the pseudogap.

Abstract:
The phase of the rotating order parameter in rotating antiferromagnetism is calculated using a combination of mean-field theory and Heisenberg equation. This phase shows a linear time dependence, which allows us to interpret rotating antiferromagnetism as a synchronized Larmor-like precession of all the spins in the system or as an unusual ${\bf q}=(\pi,\pi)$ spin-wave around a zero local magnetization. We discuss implications for the pseudogap state of high-$T_C$ superconducting materials. Rotating antiferromagnetism has been proposed to model the pseudogap state in these materials.

Abstract:
Using the U(1) holon pair slave boson theory [Phys. Rev. B 64, 052501 2001)], we derive a low energy field theory of dealing with both d-wave superconductivity and antiferromagnetism for underdoped cuprates by constructing both the Cooper pair field and the chargon pair field. In terms of the internal gauge field, the Cooper pair field carries no internal charge while the chargon pair field carries the internal charge. They are decoupled in the low energy limit. This allows us to separately treat the XY model of the Cooper pair field to describe superconductivity and the Abelian Higgs model of the chargon pair field to describe antiferromagnetism in the presence of Dirac fermions at and near the d-wave nodal points. Thus we find that the d-wave superconductivity can coexist with antiferromagnetism and that despite the coexistence, the antiferromagnetism can not affect the superconducting transition, thus allowing the XY universality class in the extreme type II limit.

Abstract:
We propose that the enigmatic pseudogap phase of cuprate superconductors is characterized by a hidden broken symmetry of d(x^2-y^2)-type. The transition to this state is rounded by disorder, but in the limit that the disorder is made sufficiently small, the pseudogap crossover should reveal itself to be such a transition. The ordered state breaks time-reversal, translational, and rotational symmetries, but it is invariant under the combination of any two. We discuss these ideas in the context of ten specific experimental properties of the cuprates, and make several predictions, including the existence of an as-yet undetected metal-metal transition under the superconducting dome.

Abstract:
We represent the superconducting ceramic compounds by the single band extended Hubbard model. We solve this model for the simultaneous presence of antiferromagnetism and the d-wave superconductivity in the Hartree-Fock (H-F) and in the coherent potential (CP) approximation, which is applied to the on-site Coulomb repulsion U. The hopping interaction used in addition to the Coulomb repulsion causes rapid expansion of the band at carrier concentrations departing from unity. This expansion shifts the d-wave superconductivity away from the half filled point reducing its occupation range approximately to the experimental range in the YBaCuO compound. The CP approximation used for the Coulomb repulsion is justified by the large ratio of Coulomb repulsion to the effective width of perturbed density of states being reduced by the hopping interaction. Fast disappearance of antiferromagnetism observed experimentally is supported by the relatively large value of the total width of unperturbed density of states. It is shown that our model is capable of describing the electron doped compounds as well.

Abstract:
Using mean-field theory, we illustrate the long-range Coulomb effect on the antiferromagnetism in the electron-doped cuprates. Because of the Coulomb exchange effect, the magnitude of the effective next nearest neighbor hopping parameter increases appreciably with increasing the electron doping concentration, raising the frustration to the antiferromagnetic ordering. The Fermi surface evolution in the electron-doped cuprate Nd$_{2-x}$Ce$_x$CuO$_4$ and the doping dependence of the onset temperature of the antiferromagnetic pseudogap can be reasonably explained by the present consideration.