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The effect of nonmagnetic impurities and the effective masses on the spin-dependent transport in a ferromagnet-normal metal-ferromagnet junction is investigated on the basis of a two-band model. Our results show that impurities and the effective masses of electrons in two ferromagnetic electrodes have remarkable effects on the behaviors of the conductance, namely, both affect the oscillating amplitudes, periods, as well as the positions of the resonant peaks of the conductance considerably. The impurity tends to suppress the amplitudes of the conductance, and makes the spin-valve effect less obvious, but under certain conditions the phenomenon of the so-called impurity-induced resonant tunneling is clearly observed. The impurity and the effective mass both can lead to nonmonotonous oscillation of the junction magnetoresistance (JMR) with the incident energy and the thickness of the normal metal. It is also observed that a smaller difference of the effective masses of electrons in two ferromagnetic electrodes would give rise to a larger amplitude of the JMR. [ABSTRACT FROM AUTHOR]

The one-dimensional spin-one Heisenberg antiferromagnet with single-ion anisotropy in the presence of the applied magnetic field is explored in terms of the Schwinger boson mean-field theory. The temperature and anisotropy dependences of the specific heat, the susceptibility and the magnetization are thoroughly discussed. New features of the specific heat as a function of temperature as well as anisotropy are found. A transition from an antiferromagnetic phase to a spin-canting phase is observed, and meanwhile, a schematic phase diagram is proposed. [ABSTRACT FROM AUTHOR]

The relationship between the Fermi surface (FS) and the symmetry of the gap function in unconventional superconductors is argued. It is found that the shapes of the FS are indeed related to the symmetry of the superconducting gap function, and is also influenced by the next nearest-neighbor overlapping. The application of the arguments to cuprate superconductors is briefly discussed. There is observed an interesting property that Luttinger's theorem perfectly holds for various pure gap symmetries in the weak-coupling limit while it is violated for d[sub x²-y²]- and d[sub x²-y²] + id[sub xy]-wave symmetries in a few cases. [ABSTRACT FROM AUTHOR]

It can be shown that the bosonic degree of freedom of the tightly bound on-site electron pairs could be separated as Schwinger bosons. This is implemented by projecting the whole Hilbert space into the Hilbert subspace spanned by states of two kinds of Schwinger bosons (to be called binon and vacanon) subject to a constraint that these two kinds of bosonic quasiparticles cannot occupy the same site. We argue that a binon is actually a kind of quantum fluctuations of electron pairs, and a vacanon corresponds to a vacant state. These two bosonic quasiparticles may be responsible for the Bose-Einstein condensation (BEC) of the system associated with electron pairs. These concepts are also applied to the attractive Hubbard model with strong coupling, showing that it is quite useful. The relevance of the present arguments to the existing theories associated with the BEC of electron pairs is briefly commented. [ABSTRACT FROM AUTHOR]