Chang-De Gong

Numerical investigation of light-wave localization in optical Fibonacci superlattices with symmetric internal structure

We study numerically the optical transmission of one-dimensional binary quasiperiodic dielectric multilayers, which are arranged in Fibonacci sequences along two opposite directions and possess a mirror symmetry. We find that the transmission coefficient is unity for all sequences studied at the central wavelength = 0, where 0 = 4nA (B)dA (B), with nA (B) and dA (B) being the index of refraction and thickness of two kinds of layer, respectively. As the number of layers in the sequence increases, more and more perfect transmission peaks appear. We observe a scaling of the transmission spectra with increasing sequence length. These phenomena will find applications in fabrication of multiwavelength narrow-band optical filters.

The study of spin-spin correlations in quasi-one-dimensional Heisenberg antiferromagnetic clusters

For a class of quasi-one-dimensional clusters, by using exact diagonalization, we study the effect of side spins on the spin-spin correlations on the chain. Our calculations show that side spins added in the same sublattice can effectively strengthen the spin-spin correlations in the large-distance region and make the change tend to flatten. It is exactly proved that periodically adding side spins can set up magnetic long-range order in the ground state. We also investigate the effect of the density of side spins on correlation strength. The case where two sublattices have different localized spins is discussed.

Interaction effects and dimensional crossover in disordered tunnelling superlattices

Effects of mutual interactions on the conductivity tensor and the density of states have been studied in the weakly localized regime of disordered tunnelling superlattices. The analytical results for the interaction corrections to both quantities are obtained as functions of the interlayer coupling t and the temperature T. The authors show that the temperature dependences of both corrections change from three-dimensional to two-dimensional behaviour with decreasing t, and that the dimensional crossover occurs at t approximately 1/ tau 0, with tau 0 the relaxation time due to impurity scattering.

Transverse freezing in the infinite-range quantum Ising spin glass with transverse and Gaussian random longitudinal fields

The infinite-range quantum Ising spin glass in a transverse and a Gaussian random field has been studied by combining the pair approximation with the discretized path-integral representation. The phase diagrams are obtained, and the possibilities of the existence of a mixed phase in which ferromagnetism and spin-glass order coexist are discussed. This is expected to interpret some properties of the mixed hydrogen-bonded ferroelectric and antiferroelectric crystals such as Rb1-x(NH)4xH2PO.

Superconductivity in doped planar CuO2 systems

The authors present a model to describe high-Tc superconductivity in doped planar CuO2 systems. Each doped hole on the oxygen site interacts through strong antiferromagnetic (AF) coupling with two neighbouring copper holes to form Cu-O spin singlet pairs and interacts with a Cu-RVB state to lead to the condensation of O holes in momentum space, which is responsible for the superconductivity. The ground state of this system and the spin correlation of Cu and O holes are also studied. The results are in good agreement with previous works.

Softened spin-wave dispersion and sublattice magnetization at finite temperature for a three-dimensional anisotropic Heisenberg antiferromagnet

We study a three-dimensional anisotropic quantum antiferromagnetic Heisenberg model at finite temperature in which the interplanar coupling can be varied gradually. With the magnon interactions considered, we have calculated the spin-wave excitation and sublattice magnetization. We find that when the interplanar coupling increases, the Neel ordered state is stabilized gradually. Moreover, we find power laws at low temperatures: a T4-law for the spin-wave excitation, and a T2-law for the sublattice magnetization, which is consistent with the nuclear magnetic resonance experiments on antiferromagnets. The interplanar coupling dependences of the finite-temperature spin-wave excitation and magnetization are also given.

Interacting Boson Approach to the Low-Dimensional Quantum Antiferromagnets: a Variational Monte–Carlo Study*

We present a spin- antiferromagnetic Reisenberg model in an interacting boson representation exactly by using modified Holstein–Primakoff transformation. For interacting boson systems on one-dimensional linear chains and square lattices, we perform Monte–Carlo calculations using the well-established Jastrow-type trial wavefunction. We find that the ground state energies and spin correlations agree well with other numerical and theoretical results.

Multifractality of a Cartesian Product of Two Fractals

We discuss fractal measures on a bifractal, which is defined as a Cartesian product of two fractals and represents a class of self-affine fractals. It is shown that the global and are the sums of the corresponding exponents for the subfractals. The relation between the global spectrum and those for subfractals is also derived.

Effect of Inelastic Scattering on the Electron Transport in a One-Dimensional Electron Interferorneter*

Using the Buttiker formalism, we calculated the conductance of a one-dimensional interferometer,which consists of two quantum point contacts (QPCs) and a cavity sandwiched between them, in the presence of a phase randomizing scatterer located at the lower boundary of the cavity. The results show that a little inelastic scattering will completely destroy the formation of discrete zero-dimensional states, but the Aharonov-Bohrn-type oscillations can still take place, which are influenced by the inelastic scatterer.

Scaling Investigations on Dynamics of a Homogeneity-Fractal Mixed Structure

Several dynamical properties on a homogeneity-fractal-mixed structure are explored by scaling methods. We discuss random diffusions, vibrational excitations and its scattering by structural irregularities.