Gong Chang-De

Light Transmission Through Symmetric Fibonacci-Class Multilayers

We have studied the optical transmission of one-dimensional Fibonacci-class quasiperiodic multilayers, which possess a mirror symmetry. We find that the transmission coefficient is unity for all studied sequences at the central wavelength λ = λ0, where λ0 = (1/4)nA(B)dA(B) with nA(B) and dA(B) being the index of refraction and thickness of two kinds of layers, respectively. Two-cycle or three-cycle has been found around λ = λ0, which is different from the features of the sequences without symmetric structure.

Possibility of Coexistence of Ferromagnetism and Superconductivity in an Anisotropic Quasi-Two-Dimensional System

Possibility of coexistence of ferromagnetism (FM) and superconductivity (SC) in UGe2 based on a two-parameter model in an anisotropic quasi-two-dimensional system is discussed with both singlet s-wave and triplet p-wave SCs. It is emphasized that the coexistence of FM and singlet s-wave SC is energetically high among all possible states, while the coexistence of FM and triplet p-wave SC is energetically favourable among all possible states. Furthermore, we find that the magnetization dependence of the SC energy gap is nonmonotonic, which may explain the experimental result discovered in UGe2.

Low-Density Ferromagnetism in the Hubbard Model

We study analytically the stability of the saturated ferromagnetic ground state (the Nagaoka state) of the Hubbard model in the low electron density limit with the mean-field approach. We find that the critical Uc is just 4?t, where t is the hopping integral between the nearest neighbours, i.e., when U is larger than 4?t, the paramagnetic state is unstable with respect to the ferromagnetic state, and vice versa. PACS: ?75.?30.?Kz, 71.?10.?Fd

Competition Between Two Ordering Processes in Two-Dimensional Doped Antiferromagnets

We provide a Landau theory of the coupled charge density wave and spin density wave order parameters to investigate the possibility of coexistence or competition between the two ordering processes occurring in the two-dimensional doped antiferromagnet. We find that the two ordering processes can coexist only in a certain region of coupling parameters, and the one with lower transition temperature can only coexist together with the other one with higher transition temperature and cannot be stabilized separately. Phase diagrams in different situations are given.

An Extended Landauer Conductance Formula in High-Dimensional Case

A Landauer-like formula of high-dimensional conductance is obtained. As before, conductance is expressed by the averaged transmission and reflection coefficients, but with correction from dimensionality and material properties. As an application, we have obtained the length dependence of conductivity under two different conditions.

Interaction Between Two Holes in the CuO2 Plane of Cuprate Superconductors

We have studied the behavior of two holes in the CuO2 plane of cuprate superconductors which is important for making clear the origin of the superconductivity. The interaction between two holes does not show a simple form but a damped oscillating function of the distance between them. It is favorable for them to get closer with a distance about five or ten lattice constant just by thermal motion. Around the equilibrium positions, the vibration motion is considered.

Evidence of Phase Separation in the Hubbard Model

We examine theoretically the possibility of phase separation due to hole aggregation in the background of anti-ferromagnetically ordered CuO2 planes. The results which are calculated within a self-consistent mean-field-type approximation give obvious evidence of phase separation. Our conclusions agree with previous numerical results (from exact diagonalization).

Absence of Localization in One-Dimensional Lattice with Off-Diagonal Nonlinearity Disorder

The time evolution of an initially localized mode in a one-dimensional lattice with off-diagonal nonlinearity disorder is studied by solving a modified nonlinear Schrodinger equation. Absence of localization is found when the nonlinearity parameter is beyond the self-trapping region for corresponding periodic lattice. The propagation of electrons shows ballistic behavior even in the presence of disorder. When self-trapping occurs, the untrapped portion still escapes ballistically.

Replica Symmetry Breaking in Critical Phenomena in Long-Range Disordered Ferromagnets

The replica symmetry breaking (RSB) is investigated in -component ferromagnetic spin systems with a long-range disorder, with a correlation function obeying a power law . The Landau–Ginzburg Hamiltonian with an RSB quartic interaction term is studied, with the renormalization-group expansion in and , where is the spatial dimension. It is shown that the long-range disorder fixed point found previously is unstable under the perturbation of RSB for and stable for . The RSB fixed points are calculated and there is no physical stable fixed point for .

Continuous Replica Symmetry Breaking in Critical Phenomena in Disordered Ferromagnets

The replica symmetry breaking (RSB) in critical phenomena in disordered ferromagnets is studied. We modified the assumption of Dotsenko et al. about the local minimum solutions of the Hamiltonian with random temperature. It is shown explicitly that the continuous RSB is generated in the renormalization group (RG). The physical regime of the coupling constants are investigated through the RG equations.