Properties of the ground state in a spin—2 transverse Ising model with the presence of a srystal field

The properties of the ground state in the spin-2 transverse Ising model with the presence of a crystal of a crystal field are studied by using the effective-field theory with correlations,The longitudinal and transverse magnetizations,the phase diagram and the internal energy in the ground state are given numerically for a honeycomb lattice(z=3).     

Statistical properties of the one dimensional Anderson model relevant for the nonlinear Schrödinger equation in a random potential

The statistical properties of overlap sums of groups of four eigenfunctions of the Anderson model for localization as well as combinations of four eigenenergies are computed. Some of the distributions are found to be scaling functions, as expected from the scaling theory for localization. These enable to compute the distributions in regimes that are otherwise beyond the computational resources. These distributions are of great importance for the exploration of the nonlinear Schrödinger equation (NLSE) in a random potential since in some explorations the terms we study are considered as noise and the present work describes its statistical properties.     

The possibility of a compensation point induced by a transverse field in transverse Ising nanoparticles with a negative core–shell coupling

The phase diagram and magnetizations of two 2D nanoparticles with a negative core–shell interaction, described by the transverse Ising model, are investigated by the use of the effective field theory with correlations. The behaviors of a compensation point in these nanosystems are examined by changing an applied transverse field. It is proved that a compensation point can be induced in the two nanosystems by applying a transverse field.     

Squeezing in a three-level Jaynes-Cummings model with strong field

Squeezing in three-level Jaynes-Cummings model with the strong initial coherent state is studied numerically. The dependence of the squeezing on the field intensity and time is analysed. The cases that the light field is initially in a Fock state and in a squeezed vacuum state are also discussed.     

Spin-1 Blume–Capel model with random crystal field effects

The random-crystal field spin-1 Blume–Capel model is investigated by the lowest approximation of the cluster-variation method which is identical to the mean-field approximation. The crystal field is either turned on randomly with probability p$p$ or turned off with q=1−p$q=1-p$ in a bimodal distribution. Then the phase diagrams are constructed on the crystal field (Δ$\Delta$)–temperature (kT/J)$(kT/J)$ planes for given values of p$p$ and on the (kT/J,p$kT/J,p$) planes for given Δ$\Delta$ by studying the thermal variations of the order parameters. In the latter, we only present the second-order phase transition lines, because of the existence of irregular wiggly phase transitions which are not good enough to construct lines. In addition to these phase transitions, the model also yields tricritical points for all values of p$p$ and the reentrant behavior at lower p$p$ values.     

On the ground-state threshold in random two-dimensional Ising ±J models

For square, triangular, and for hexagonal lattices there is numerical and theoretical support that the ground-state thresholdp _c between ferro- and paramagnetism in random 2D Ising ±J models, withp as the concentration of antiferromagnetic bonds, is identical top ^*which is characterized by minimal matching properties of frustrated plaquettes. From square lattices of size 100×100 we have got p_c,sq<0.117 by simulations which produced average groundstate magnetizations per spin by means of exact minimal matchings. Moreover, from the squareL×L-lattices treated (L = 10, 20, 50, 100) we obtained the estimatep _c,sq 0.1 which is in agreement with the Grinstein estimatep _c,sq 0.099 andp _c,sq 0.105 by Freund and Grassberger.     

Contribution of the inelastic channels K − p → Yπ to the shift of the ground-state energy level of kaonic hydrogen

The contribution of the inelastic channels K ^? p → Yπ, where Yπ = Σ^? π ⁺, Σ ⁺ π ^?, Σ ⁰ π ⁰, or λ⁰ π ⁰, kinematically allowed at the K ^? p threshold to the S-wave scattering length of elastic K ^? p scattering, as well as the shift of the ground-state energy of kaonic hydrogen, is calculated. The result, δa ₀ ^K?p = ?0.037 ± 0.010 fm and δε _1s = 15 ± 4 eV, will be important for the theoretical analysis of the expected data from the experiments scheduled by the DEAR and SIDDHARTA Collaborations at the end of 2006.     

Inverse transitions in the Ghatak–Sherrington model with bimodal random fields

The present work studies the Ghatak–Sherrington (GS) model in the presence of a longitudinal magnetic random field (RF) _hi$h_i$ following a bimodal distribution. The model considers a random bond interaction _Ji,j$J_{i,j}$ which follows a Gaussian distribution with mean _J0/N$J_0/N$ and variance J²/N$J^2/N$. This allows us to introduce the bond disorder strength parameter J/_J0$J/J_0$ to probe the combined effects of disorder coming from the random bond and the discrete RF over unusual phase transitions known as inverse transitions (ITs). The results within a mean field approximation indicate that these two types of disorder have completely distinct roles for the ITs. They indicate that bond disorder creates the necessary conditions for the presence of inverse freezing, or even inverse melting, depending on the bond disorder strength, while the RF tends to enforce mechanisms that destroy the ITs.     

Seebeck-effect in the mixed state of Y−Ba−Cu−O

We report on measurements of the Seebeck-effect, the Nernst-effect, and the magnetoresistance in the mixed state of ac-axis oriented expitaxial film of Y–Ba–Cu–O. In contrast to conventional superconductors we find a large Seebeck-coefficientS, which is comparable in magnitude to the Nernst-effect. The broadening of the super-conducting transitions of magnetoresistance and Seebeck-effect are rather similar with respect to (1) the temperature dependence, (2) the dependence on the direction between magnetic field and crystal axis and (3) the dependence on the direction between magnetic field and driving forces. The large Seebeck-effect has to be attributed to dissipation due to normal quasiparticle-excitations, since the vortex-contribution to the Seebeck-effect is by far too small to account for the observed magnitude ofS. It is argued that such a quasiparticle contribution to the dissipation is large in the high-T _c superconductors because of the small coherence lengths and thus the small vortex cores. Another possibility is that granularity leads to dissipation proportional to the normal state transport properties. The Seebeck-voltage depends on all dissipative processes other than vortex motion, whereas the Nernst-effect depends only on the vortex motion. Therefore by measurements of thermomagnetic effects the various dissipative properties may be separated.     

Spectrum of a scalar field in a Gödel cosmological model

A study is made of the spectrum of a scalar field for the general case of a causal metric of the Gödel type. Its substantial difference from the spectrum of a noncausal metric is demonstrated. In a causal metric, the spectrum of scalar particles is divided into three regions: 1) a region of low energy and a discrete spectrum; 2) a region of intermediate energy and a continuous spectrum, with the same dispersion relation; 3) a region of high energy and likewise a continuous spectrum, but with a different dispersion relation. In the latter case, the dispersion relation is symmetrical with respect to a sign change of the particle energy , whereas in the first two cases symmetry is conserved only for a simultaneous sign change of both and the projection of the orbital moment onto the z axis. For nonzero mass and a quite low z component of the particle momentum, the upper and lower continua of the states merge, and the energy gap disappears.St. Petersburg University of Economics and Finance. Translated from Izvestiya Vysshikh Zavedenii, Fizika, No.9, pp. 39–43, September, 1993.     

Energy-momentum tensor of a spinor field in the “mixed universe” cosmological model

The energy-momentum tensor of a massless spinor field is constructed and studied based on the previously proposed interpretation of quantum effects of such a field in the anisotropic metric of Bianci type IX. The characteristic properties of the energy-momentum tensor in the mixed universe model are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 45–50, September, 1988.I am grateful to A. A. Grib and A. V. Nesteruk for their interest in this work and for useful discussions.     

Atomic coherent trapping and phase property of the field in the system of two-level atoms interacting with a single-mode field

In this paper,the condition of the atomic coherent trapping in the system of twotwo-level atoms interacting with a single-mode coherent field has been obtained.And proper-ties of the light field in this case has also been analysed by means of the phase theory intro-duced by Barnett and Pegg,     

Drift−diffusion model of normal glow discharge in an axial magnetic field

A two-dimensional axisymmetrical computing model is formulated with using of which the mathematical modeling of the normal glow discharge in molecular hydrogen is fulfilled in an axial magnetic field with the induction B = 0.1 T in the pressure range p = 1.25?5 Torr and the current-source electromotive force E = 1?3 kV.     

Bound fermion states in the field of a soliton of the nonlinear O(3) σ model

The (2 + 1)-dimensional nonlinear O(3) σ model whose n field is coupled to the fermion field by the Yukawa interaction has been examined. The cases of the isosinglet and isodoublet fermion fields with respect to the internal symmetry group have been considered. It has been shown that bound states of the fermion in the n field of a soliton of the nonlinear O(3) σ model exist for some variants of the Yukawa interaction. The absence of zeroth fermion modes in the n field of the soliton has been established. The properties of the ground state of the fermion have been numerically studied. In particular, it has been shown that an increase in the spatial size of the soliton results in a decrease in the energy of the ground state. This leads to the instability of the soliton in a certain region of the parameters of the model.     

Critical behavior and phase diagrams of a spin-1 Blume–Capel model with random crystal field interactions: An effective field theory analysis

A spin-1 Blume–Capel model with dilute and random crystal fields is examined for honeycomb and square lattices by introducing an effective-field approximation that takes into account the correlations between different spins that emerge when expanding the identities. For dilute crystal fields, we have given a detailed exploration of the global phase diagrams of the system in _kBTc/J−D/J$k_B{T}_c/J-D/J$ plane with the second and first order transitions, as well as tricritical points. We have also investigated the effect of the random crystal field distribution characterized by two crystal field parameters D/J$D/J$ and △/J$△/J$ on the phase diagrams of the system. The system exhibits clear distinctions in a qualitative manner with coordination number q$q$ for random crystal fields with △/J,D/J≠0$△/J,D/J\ne 0$. We have also found that, under certain conditions, the system may exhibit a number of interesting and unusual phenomena, such as reentrant behavior of first and second order, as well as a double reentrance with three successive phase transitions.     

Linear entropy dynamics of the field in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation

We present the linear entropy dynamics of the field state in the dispersive cavity in the Jaynes－Cummings model with an intensity-dependent coupling in the dispersive approximation, and investigate the influence of dissipation on entanglement between the field and the atoms. We show that the coherence properties of the field are also affected by the cavity when the nonlinear process of the field interacting with the atoms with an intensity-dependent coupling is involved, and find that the dissipation constant, the intensity of the field and the atomic distribution angle have different influence on the coherence properties of the field.     

The ising model in a magnetic field of ½iπ

The result of Lee and Yang for the free energy of a square two-dimensional Ising model in a magnetic field of ½iπ is shown to be correct only if the thermodynamic limit is approached through even numbers of lattice sites. Derivations of this result are given by the algebraic (Onsager-Kaufman) method and the fermion operator (Hurst) method.     

Decay of correlations in the one dimensional Ising model withJ ij =|i−j|−2

A low temperature expansion is constructed for the one dimensional Ising model with Hamiltonian . It is shown that the two point function _i ; _j obeys upper and lower bounds of the formf()|i–j|^–2 for inverse temperature sufficiently large.Junior Fellow, Harvard University Society of Fellows. Supported in part by the National Science Foundation under Grant No. PHY79-16812.