A partial charge-spin separation fermion-spin theory is developed to study the normal-state properties of the underdoped cuprates. In this approach, the physical electron is decoupled as a gauge invariant dressed holon and spinon, with the dressed holon behaving like a spinful fermion, representing the charge degree of freedom together with the phase part of the spin degree of freedom, while the dressed spinon is a hard-core boson, representing the amplitude part of the spin degree of freedom. The electron local constraint for the single occupancy is satisfied. Within this approach, the charge and spin dynamics of the underdoped cuprates are studied based on the t-t ′ -J model. It is shown that the charge dynamics is mainly governed by the scattering from the dressed holons due to the dressed spinon fluctuation, while the scattering from the dressed spinons due to the dressed holon fluctuation dominates the spin dynamics. 74.25.Fy, 74.25.Ha,

Within the t-t ′ -J model, the electron spectrum and quasiparticle dispersion in doped bilayer cuprates in the normal state are discussed by considering the bilayer interaction. It is shown that the bilayer interaction splits the electron spectrum of doped bilayer cuprates into the bonding and antibonding components around the [π, 0] point. The differentiation between the bonding and antibonding components is essential, which leads to two main flat bands around the [π, 0] point below the Fermi energy. In analogy to the doped single layer cuprates, the lowest energy states in doped bilayer cuprates are located at the [π/2, π/2] point. Our results also show that the striking behavior of the electronic structure in doped bilayer cuprates is intriguingly related to the bilayer interaction together with strong coupling between the electron quasiparticles and collective magnetic excitations.

Within the microscopic theory of the normal-state pseudogap state, the doping and temperature dependence of the charge dynamics in doped cuprates is studied in the whole doping range from the underdoped to heavily overdoped. The conductivity spectrum in the underdoped and optimally doped regimes contains the low-energy non-Drude peak and unusual midinfrared band. However, the position of the midinfrared band shifts towards to the low-energy non-Drude peak with increasing doping. In particular, the low-energy non-Drude peak incorporates with the midinfrared band in the heavily overdoped regime, and then the low-energy Drude behavior recovers. It is shown that the striking behavior of the low-energy non-Drude peak and unusual midinfrared band in the underdoped and optimally doped regimes is closely related to the emergence of the doping and temperature dependence of the normal-state pseudogap.Comment: 9 pages, 6 figures, added discussions and references, accepted for publication in Physica C. arXiv admin note: text overlap with arXiv:1109.397

It has been suggested that either the diamagnetism or paramagnetism of Bose gases, due to the charge or spin degrees of freedom respectively, appears solely to be extraordinarily strong. We investigate the magnetic properties of charged spin-1 Bose gases in an external magnetic field, focusing on the competition between the diamagnetism and paramagnetism, using the Lande-factor g of particles to evaluate the strength of the paramagnetic effect. We propose that a gas with g < 1/√8 exhibits diamagnetism at all temperatures, while a gas with g > 1/2 always exhibits paramagnetism. Moreover, a gas with the Lande-factor in between shows a shift from paramagnetism to diamagnetism as the temperature decreases. The paramagnetic and diamagnetic contributions to the total magnetization density are also calculated in order to demonstrate some details of the competition.

Within the framework of the kinetic energy driven superconductivity, the electronic structure of bilayer cuprate superconductors in the superconducting state is studied. It is shown that the electron spectrum of bilayer cuprate superconductors is split into the bonding and antibonding components by the bilayer splitting, and the observed peak-dip-hump structure around the ͓ ,0͔ point is mainly caused by this bilayer splitting, with the superconducting peak being related to the antibonding component and the hump being formed by the bonding component. The spectral weight increases with increasing doping concentration. In analogy to the normal-state case, both electron antibonding peak and bonding hump have the weak dispersions around the ͓ ,0͔ point.