Novel metallic behavior in two dimensions

Experiments on a sufficiently disordered two-dimensional (2D) electron system in silicon reveal a new and unexpected kind of metallic behavior, where the conductivity decreases as sigma(n(s),T) = sigma(n(s),T = 0)+A(n(s))T(2) (where n(s) is carrier density) to a nonzero value as temperature T-->0. In 2D, the existence of a metal with dsigma/dT>0 is very surprising. In addition, a novel type of a metal-insulator transition obtains, which is unlike any known quantum phase transition in 2D.     

A Note on the Quantum Widom–Rowlison Model

Using the renormalization methods we show that the symmetry breaking in the quantum Widom–Rowlison model of particles obeying Boltzmann statistics occurs at any value of the inverse temperature >0 once the activity of the particles is sufficiently large.     

Finite temperature SU(2) lattice gauge theory

We discuss SU(2) lattice gauge theories at non-zero temperature and prove several rigorous results including i) the absence of confinement for sufficiently high temperature in the pure gauge theory, and ii) the absence of spontaneous chiral symmetry breaking for sufficiently high temperature in the theory with massless fundamental representation fermions.     

Lorentz transformation on the lattice

We study the possibility of representing the kinematical variables of a free particle in terms of scale factors and integers. The action of a set of transformations from the Lorentz group parametrized by integers on this system of variables are investigated, and it is shown that one can effectively characterize these symmetries on a lattice in this way. By taking the scales sufficiently small, one can arbitrarily closely approach the continuous case.Work supported in part by the Binational Science Foundation (BSF) Jerusalem. Israel.     

Low temperature expansions for the Gibbs states of weakly interacting quantum Ising lattice systems

Low temperature expansions for the Gibbs states of weakly interacting transverse Ising-like models are developed, by conditioning the states on a sub-algebra of observables. The conditioned states have effective classical Hamiltonians which are estimated by the solution to a simple implicit equation. Provided the interaction is sufficiently weak but fixed independent of temperature, and the temperature is sufficiently low, exponential clustering of the correlation functions holds.     

Casimir Effect at Finite Temperature in the Presence of One Fractal Extra Compactified Dimension

We discuss the Casimir effect for massless scalar fields subject to the Dirichlet boundary conditions on the parallel plates at finite temperature in the presence of one fractal extra compactified dimension. We obtain the Casimir energy density with the help of the regularization of multiple zeta function with one arbitrary exponent and further the renormalized Casimir energy density involving the thermal corrections. It is found that when the temperature is sufficiently high, the sign of the Casimir energy remains negative no matter how great the scale dimension δ is within its allowed region. We derive and calculate the Casimir force between the parallel plates affected by the fractal additional compactified dimension and surrounding temperature. The stronger thermal influence leads the force to be stronger. The nature of the Casimir force keeps attractive.     

On the concept of attractor

This note proposes a definition for the concept of attractor, based on the probable asymptotic behavior of orbits. The definition is sufficiently broad so that every smooth compact dynamical system has at least one attractor.     

Phase transitions in lattice gas models for water

Water-like lattice gases on the triangular and body-centered cubic lattices are investigated. Molecules may reside on the lattice sites in either of two possible orientations, a hydrogen bond being formed between molecules on neighboring sites if they have the proper orientation with respect to one another. For a range of chemical potential at sufficiently low temperatures, the models are shown to have an ordered phase consisting of an open, hydrogen-bonded, icelike structure. The models are shown to be transitionfree at sufficiently high temperature, indicating the existence of a critical point.Research supported in part by the U.S. National Science Foundation, Grant CHE-7726177, and by The Robert A. Welch Foundation, Grant P-446.     

Instabilities due to negative pressure effects

The presence of a negative pressure component in a plasma causes low frequency electrostatic ion waves to become unstable if the number density of that component is sufficiently high or its temperature sufficiently low.     

On the influence of exciton-exciton interaction on the critical temperature of Bose-Einstein condensation

Under the assumption of a sufficiently large concentration of a weakly repulsive interacting exciton system the realization of the superfluid state of this system is theoretically possible. This paper deals with the influence of the interaction on the critical temperature of the Bose-Einstein condensation with application to the case of the lowest exciton states in a benzene crystal using previous results (Majerníková E.: Czech. J. Phys.B 18 (1968), 830). It has been found that this interaction causes a rapid decrease of the critical temperature.The author wishes to thank Prof. M. Trlifaj for his useful suggestions.     

First inelastic neutron scattering studies on thin free standing polymer films

Glass transition studies in free standing polymer films have revealed values of the transition temperature, T(g), which were substantially reduced below the bulk for sufficiently thin films. Here we report on the preparation of two stacks of free standing polystyrene films: 70 films with a thickness of h approximately 107 nm and 140 films with h approximately 55 nm with equivalent total sample thicknesses of approximately 7.5 microm. We have performed the first measurements on such samples using inelastic neutron scattering, and demonstrate that inelastic neutron scattering experiments, performed on the time-of-flight spectrometer IN6 and the backscattering spectrometer IN16 at the Institut Laue-Langevin, are feasible.     

Stability of quark gluon plasma to nielsen-olesen mode

Nielsen and Olesen showed that perturbative vacuum with uniform chromomagnetic field in one space and one color direction is unstable. This instability is called Nielsen-Olesen instability (NOI), and leads to formation of a ‘spaghetti of flux tubes’ as a model for non-perturbative vacuum and confinement. We re-examine this instability in presence of color sources, quarks and gluons, at a finite temperature and find that at sufficiently high temperature NOI is stabilized due to an ‘effective mass’ of gluons arising through plasma effects. This explains how a QGP with no confinement effects may exist at high temperature. As the temperature is lowered, NOI reappears at a valueT=T _c, which is very close to confinement-deconfinement transition from hadrons to QGP..     

Contribution of vaporization and boiling to thermal-spike sputtering by ions or laser pulses

Here we consider what, in our terminology, we designate as normal vaporization, normal boiling, and phase explosion. In the case of vaporization, one is dealing with the emission of particles (atoms or molecules) from the extreme outer surface of either a solid or liquid for any temperature exceeding 0 K. In the case of boiling, one is (at least ideally) dealing with heterogeneously nucleated bubbles which diffuse to the outer surface of a liquid or solid and then escape, the latter being possible for temperatures equal to or exceeding the boiling temperature (T(b)). In the case of phase explosion one is dealing with the consequences of what happens when a liquid approaches the thermodynamic critical temperature (T(tc) or T(c)), and massive homogeneous nucleation takes place. Although these three mechanisms have been reviewed in reasonable detail in recent work, we will here present evidence, apparently not previously considered, that boiling, whether the distance scale is atomically small (5-15 nm, as for laser-pulse impact on a metal in the absence of thermal diffusion) or much larger, has a prohibitive kinetic obstacle because it requires bubble diffusion if the bubbles are formed other than at the outer surface. That is to say, boiling will never be a significant process whether with ion or laser-pulse impact. This leaves vaporization and phase explosion as the only possible thermal-spike processes capable of expelling material from an ion- or laser-pulse bombarded surface in a significant quantity. But even with vaporization it can be shown that a kinetic obstacle, although not as severe as for boiling, will enter. The final result is that only phase explosion will normally be relevant for sufficiently short time scales.     

Average mutual information of the random block-message ensembles for many-letters

By making use of the theoretical framework presented by Bostroem(K.J.Bostroem,LANL quant-ph/0009052),we generalize the standard quantum information theory of block messages with fixed block length to the variable one.We show that the states belonging to a sufficiently large hilbert space are the highly distinguishable states.We also consider the collection states (product states of more than one qubit state) and seek a “pretty good measurement” (PGM) with measurement vectors to improve the mutual information.The average mutual information over random block-message ensembles with variable block length n is discussed in detail.     

High temperature expansions and dynamical systems

We study continuous and discrete spin systems on a lattice with random interactions of finite range. In particular for sufficiently large interactions we prove no spectral gap property in the high temperature region. Moreover we show that in two dimensions, if the temperature is sufficiently high and the probability of interaction to be large is small enough, we have an almost sure stretched exponential upper bound for the decay to equilibrium.Supported by EEC grant SC1-CT92-784.     

Magnetic susceptibility and electrical resistivity of Ni-Al alloys at high temperatures

Magnetic susceptibility and electrical resistivity of the Ni-Al alloy system are studied in wide temperature (700–800°C) and concentration (up to 25 at. %) intervals. It is shown that in the region of solid solutions, temperature dependencies are sufficiently well described by a modified Curie-Weiss law, taking into account the existence of a temperature-independent contribution. For liquid alloys, calculation of the dependence of the electrical resistivity on composition is performed according to the Faber-Ziman-Evans method. Magnetic and electrical characteristics obtained are explained on the basis of a modified Anderson model, with the interaction of virtual bound states of nickel with collective valent electrons of aluminum taken into account.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 23–28, March, 1982.     

Magnetically induced thermal rectification

We consider far from equilibrium heat transport in chaotic billiard chains with noninteracting charged particles in the presence of nonuniform transverse magnetic field. If half of the chain is placed in a strong magnetic field, or if the strength of the magnetic field has a large gradient along the chain, heat current is shown to be asymmetric with respect to exchange of the temperatures of the heat baths. Thermal rectification factor can be arbitrarily large for sufficiently small temperature of one of the baths.     

Influence of correlation and temperature on the electronic structure of bulk and thin film GdN

The influence of correlation and temperature on the electronic structure of bulk and thin film GdN has been studied using the s-f model, which combines the one electron band structure with a many body procedure. The tight binding linear muffin tin orbital (TB-LMTO) method was used to obtain the one electron band structure of the system. The s-f exchange coupling constants for each band were obtained from the spin polarized band structure of the system using a mean field model. Correlation effects are found to be present in the system. However they are not sufficiently strong to cause a correlation induced splitting in the spectrum. Some bands of the thin films of GdN exhibit splitting at T=T_c and it is due to the combined effect of correlation and temperature. The conduction bands of both the bulk and the thin films of GdN exhibit a red shift with respect to temperature.     

Comparison of thermally stimulated currents from temperature-dependent and temperature-independent activation energy distributions

Thermally stimulated currents from distributions depending solely on the activation energy and from distributions depending on the ratio of energy and absolute temperature, as employed in a well known work by J. van Turnhout, are compared. It is found that for sufficiently broad distributions, the TSD current of the former scales the shape of the distribution itself while that of the latter exhibits a variety of shapes, from asymmetrical peaks having a characteristic high-temperature half-width greater than the lower one, to symmetrical ones.