International Journal of Modern Physics B

We review the structure of the spin glass phase in the infinite-range Sherrington–Kirkpatrick model and the short-range Edwards–Anderson (EA) model. While the former is now believed to be understood, the nature of the latter remains unresolved. However, considerable insight can be gained through the use of the metastate, a mathematical construct that provides a probability measure on the space of all thermodynamic states. Using tools provided by the metastate construct, possibilities for the nature of the organization of pure states in short-range spin glasses can be considerably narrowed. We review the concept of the "ordinary" metastate, and also newer ideas on the excitation metastate, which has been recently used to prove existence of only a single pair of ground states in the EA Ising model in the half-plane. We close by presenting a new result, using metastate methods, on the number of mixed states allowed in the EA model.

We study the anomalous Hall effect in paramagnetic two-dimensional electron gas (2DEG) with both linear and cubic Dresselhaus spin–orbit coupling by means of Berry connection and Berry curvature. The effect of tuning the Fermi level and of tuning the cubic coupling coefficient on the anomalous Hall conductivity have been investigated semiclassically. Our results show that a sign reversal in the anomalous Hall conductivity may appear if the cubic Dresselhaus coefficient is very large and the Fermi surface is high enough, so the cubic Dresselhaus spin–orbit coupling term cannot be neglected in this case.

Following the previous theoretical study on the open lipid membranes with edges by Tu and Ou-Yang [Phys. Rev. E68, 061915 (2003)], we show that the discocyte solution can give us several interesting open vesicles with two edges and the central singularity of this solution can be avoided in the meantime.

Quantum and classical components are blended together in this proposed theoretical model for describing multiple quantum well solar cells (MQWSC) in a p-i-n architecture. The model characteristics are: the use of transfer matrix as a quantum method for finding allowed energies in the coupled quantum wells, the connection of the absorption coefficient in the confined 2D structure to the one in the bulk semiconductor, and the treatment of the whole cell as a pseudo-homogeneous media to determine its reflectance. The resulted model is intended to be a working tool to assess electro-optical properties of MQWSC. Numerical results which relate the performance of the MQWSC to its structure are reported.

Substituting Zn for Cu is known to rapidly quench superconductivity in the doped perovskites but the mechanism behind it is still not clearly understood. Single phase YBa₂(Cu_1-xZn_x)₃O_7-δ (x = 0.0 to 0.06) samples were synthesized and characterized using XRD, wet titration, resistivity, and ac susceptibility. Angle-integrated Valence Band Photoemission and Zn K-edge XAFS results clearly show that their oxygen stoichiometry (δ) changes on Zn substitution, thereby adversely affecting the density of free charge carriers and hence the normal state resistivity and the T_c. However, the observed changes in the two happen to be too large to be accounted for solely on the basis of changes in the oxygen stoichiometry δ. We find that the Zn cation acts as a strong "impurity" scattering centre in the YBCO lattice and causes local lattice distortion (LLD). It consequently induces local magnetic moment, seen in our dc susceptibility measurements. It is thus a composite of (Δδ), LLD and possibly also magnetic pair-breaking that is responsible for the rapid quenching of the superconductivity observed with Zn doping in this system.

We have carried out thermally stimulated current (TSC) measurements on as-grown Tl₂Ga₂S₃Se layered single crystals in the temperature range 10–60 K with different heating rates of 0.6–1.5 K s¹. The data were analyzed by curve fitting, initial rise, and peak shape methods. The results were in good agreement with each other. Experimental evidence was obtained for trapping center in Tl₂Ga₂S₃Se crystal with activation energy of 11 meV. The capture cross section and concentration of the traps were found to be 1.5 × 10^-23cm² and 1.44 × 10¹⁰cm^-3, respectively. Analysis of the TSC data at different light excitation temperatures leads to a value of 18meV/decade for the traps distribution.

Anti-synchronization between different hyperchaotic systems is presented using the Chen and a new system. When the parameters of two systems are known, one can apply active synchronization method. When the parameters are unknown or uncertain, one can apply adaptive synchronization method. The simulation results verify the effectiveness of the proposed two schemes.

Statistical properties of the intensity fluctuation of a saturation laser model driven by cross-correlation additive and multiplicative noises are investigated. Using the Novikov theorem and the projection operator method, we obtain the analytic expressions of the stationary probability distribution P_st(I), the relaxation time T_c, and the normalized variance λ₂(0) of the system. By numerical computation, we discussed the effects of the cross-correlation strength λ, the cross-correlation time τ, the quantum noise intensity D, and the pump noise intensity Q for the fluctuation of the laser intensity. Above the threshold, λ weakens the stationary probability distribution, speeds up the startup velocity of the laser system from start status to steady work, and attenuates the stability of laser intensity output; however, τ strengthens the stationary probability distribution and strengths the stability of laser intensity output; when λ < 0, τ speeds up the startup; on the contrast, when λ > 0, τ slows down the startup. D and Q make the relaxation time exhibit extremum structure, that is, the startup time possesses the least values. At the threshold, τ cannot generate the effects for the saturation laser system, λ expedites the startup velocity and weakens the stability of laser intensity output. Below threshold, the effects of λ and τ not only relate to λ and τ, but also relate to other parameters of the system.

New measurements of the relative oscillator strengths of copper for the 3d¹⁰4s²S_1/2→3d¹⁰n p²P_1/2, (7 ≤ n ≤ 13), and ²P_3/2(7 ≤ n ≤ 23) series are reported. The data were acquired using the magneto-optical rotation spectroscopic technique, utilizing the linearly polarized light emitted by the 2.5 GeV electron accelerator, a 7 Tesla superconducting magnet, and a 3-meter high dispersion spectrograph with photographic detection. A quantum defect plot of the density of oscillator strengths of the discrete transitions is also presented.

In this paper, we propose an entanglement concentration protocol for unknown tripartite W class states via the detection of photons which are leaked out from the cavities. In our scheme, the atom-cavity coupling strength is smaller than the cavity decay rate. Hence, the requirement on the quality factor of the cavities is greatly relaxed. The scheme is for nonpost-selection results and the fidelity of the scheme is not affected by the detection inefficiency and atomic decay. All the processes are within the current technologies.

The electronic properties of BaCuSi₂O₆ are studied by band structure calculation based on the density functional theory within local density approximation. We find that the electronic structure and properties are dominated by the layered character of the crystal structure arising from the in plane Cu 3d and O 2p electron interactions.

The modulational instability of the coupled Gross–Pitaevskii equation (alias nonlinear Schrödinger equation), which describes two Bose–Einstein condensates trapped in an asymmetric double-well potential, is investigated. The nonlinear dispersion relation that relates the frequency and wave number of the modulating perturbations is found and its analysis shows several possibilities for the modulational stability region. Exact soliton and periodic solutions are constructed via elliptic ordinary differential equations.

The electronic structure and ferromagnetism of Sn₂Co₂O₈ and Sn₂Co₂O₇ have been investigated based on the first-principles plane-wave pseudopotential method within the generalized gradient approximation. The calculated results reveal that the oxygen vacancy plays an important role in the electronic structure and ferromagnetism. The Sn₂Co₂O₈ shows half-metallic behavior, but by introducing single oxygen vacancy, the half-metallic transits to metallic behavior. At the same time, the spin magnetic moment of every Co atom and the total magnetic moment change greatly. For Sn₂Co₂O₈ and Sn₂Co₂O₇, the total spin magnetic moments are 1.99 and 3.49 u_B, respectively.