Analytic conditions for the existence of localized electron states in linear chains with two impurities

The negative eigenvalue theorem is used to obtain an analytic result for the integrated density of electron states in several types of low-dimensional lattices with two impurities in the tight binding approximation. From this expression, analytic conditions for the existence of localized electronic states are obtained. The result is directly applicable to the problem of surface states and that of chemisorption on a linear chain.The author would like to thank Prof. Dr. L.Valenta for suggesting the problem and for constant encouragement.     

Analytic conditions for the existence of localized electron states in a linear chain with an arbitrary number of impurities

The effective Hamiltonian and the negative eigenvalue theorem are used to obtain an analytic formula for the integrated density of electron states in a linear chain with an arbitrary number of impurities within the tight binding approximation. From this formula, the analytic conditions for the existence of localized electron states lying above or below the band of states of host atoms are obtained. The way of obtaining the energies of localized states and the form of eigenvectors are also discussed.     

On the existence of KMS states

A necessary and sufficient condition for the existence of KMS states is formulated in terms of a certain left ideal in the algebraA ⁰ A.     

An interpretation of the conditions for the existence of Shockley surface states

A study is made of the Shockley surface states in a linear chain of equal atoms, joined by alternately strong bonds. If the simple MO LCAO method is used, which considers the exchange integrals between nearest neighbours and next nearest neighbours, we get the surface states for a semi-infinite chain if the stronger bond is interrupted. The connection between Shockley and Tamm surface states is shown and the hypothesis is put forward that the condition for the existence of Shockley surface states has a generally simple physical interpretation, the validity of which is proved on the models of a semi-infinite crystal studied up to now.

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On the existence of stationary states during granular compaction

When submitted to gentle mechanical taps a granular packing slowly compacts until it reaches a stationary state that depends on the tap characteristics. The properties of such stationary states are experimentally investigated. The influence of the initial state, taps properties and tapping protocol are studied. The compactivity of the packings is determinated. Our results strongly support the idea that the stationary states are genuine thermodynamic states.     

On the existence of equilibrium states in local quantum field theory

It is shown that any local quantum field theory admits thermodynamical equilibrium states (KMS-states) for all positive temperatures provided it satisfies a nuclearity condition, proposed by Wichmann and one of the authors, which restricts the admissible number of local degrees of freedom.Dedicated to E. H. Wichmann on the occasion of his 60th birthday     

On the existence of exotic and non-exotic multiquark meson states

To obtain an exact solution of a four-body system containing two quarks and two antiquarks interacting through two-body terms is a cumbersome task that has been tackled with more or less success during the last decades. We present an exact method for the study of four-quark systems based on the hyperspherical harmonics formalism that allows us to solve it without resorting to further approximations, like for instance the existence of diquark components. We apply it to systems containing two heavy and two light quarks using different quark-quark potentials. While $QQ{\bar n} {\bar n}$ states may be stable in nature, the stability of $Q\overline{Q}n {\bar n}$ states would imply the existence of quark correlations not taken into account by simple quark dynamical models.     

Sufficient conditions for the existence of bound states in a potential without spherical symmetry

We give in this paper several suffieient conditions for the existence of negative energy bound states in a purely attractive potential without spherical symmetry. These conditions generalize the condition obtained recently by K. Chadan and A. Martin (C. R. Acad. Sci. Paris290 (1980), 151), and can ensure the existence of n bound states. For the spherically symmetric case, one gets simple formulae which are also new.     

Resonant localized states and quantum percolation on random chains with power-law-diluted long-range couplings

We investigate the nature of one-electron eigenstates in power-law-diluted chains for which the probability of occurrence of a bond between sites separated by a distance r decays as p(r) = p/r(1+σ). Using an exact diagonalization scheme and a phenomenological finite-size scaling analysis, we determine the quantum percolation transition phase diagram in the full parameter space (p,σ). We show that the density of states displays singularities at some resonance energies associated with degenerate eigenstates localized in a pair of sites with special symmetries. This model is shown to present an intermediate phase for which there is classical percolation but no quantum percolation. Quantum percolation only takes place for σ < 0.78, a value larger than the corresponding one for the Anderson transition in long-ranged coupled chains with random diagonal disorder. The fractality of critical wavefunctions is also characterized.     

On the stability of time-harmonic localized states in a disordered nonlinear medium

We study the problem of localization in a disordered one-dimensional nonlinear medium modeled by the nonlinear Schrödinger equation. Devillard and Souillard have shown that almost every time-harmonic solution of this random PDE exhibits localization. We consider the temporal stability of such time-harmonic solutions and derive bounds on the location of any unstable eigenvalues. By direct numerical determination of the eigenvalues we show that these time-harmonic solutions are typically unstable, and find the distribution of eigenvalues in the complex plane. The distributions are distinctly different for focusing and defocusing nonlinearities. We argue further that these instabilities are connected with resonances in a Schrödinger problem, and interpret the earlier numerical simulations of Caputo, Newell, and Shelley, and of Shelley in terms of these instabilities. Finally, in the defocusing case we are able to construct a family of asymptotic solutions which includes the stable limiting time-harmonic state observed in the simulations of Shelley.     

On the coexistence of localized and extended electronic states in the metallic phase

It is shown that in a three-dimensional (3-D) piece of a metal with dimensions exceeding the mean free path l, the main part of electronic states is localized. The Ohm law is fulfilled due to a relatively small amount of highly conducting states. The inverse lengths of localization are uniformly distributed in the range from 2/l to zero, i.e., there is a wide set of scales in the system.     

On the stability of localized states in nonlinear field models with Lifshitz invariants

The static solutions for a nonlinear vector field in models with Lifshitz invariants are investigated. It is shown that in such systems two-and three-dimensional localized states, associated with the relaxation of the modulus of the vector field, are radially unstable. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 4, 296–298 (25 August 1998)     

On the existence of Fröhlich's long-range interactions in dipolar chains

A chain of N identical polarizable molecules interacting via dipole-dipole forces is investigated. A careful mathematical analysis results in a proof of the existence of long-range forces analogous to those described by Fröhlich for two giant dipoles which is a special case in our model. The energy spectrum is more complicated and depends on the structure constants of the system. In addition, formulas have been provided for temperature dependence of the effective interaction energy. At room temperature Fröhlich's expression underestimates the strength of the interactions by at least an order of magnitude.     

Anomalously localized states in the Anderson model

It is demonstrated that anomalously localized states (ALS) in the Anderson model, being lattice specific, are not related to any of the continuous theories. We identify the spatial structure of ALS on a lattice and calculate their likelihood. Analytical results explain peculiarities in previous numerical simulations.     

On the mathematical conditions for the existence of periodic fluctuations in non-uniform media

In many areas of mathematical physics where one is interested in the propagation of waves through non-uniform media, it is often assumed that periodic excitations result in periodic responses. This assumption is examined by rigorously investigating the existence of periodic solutions of linear hyperbolic differential equations whose coefficients vary with position and whose solution must satisfy periodic boundary or source data. It is shown that the nature of the coefficients of the undifferentiated terms of the differential system is crucial in determining whether or not the solution is periodic. In physical applications, these coefficients usually depend on the gradients of media properties as well as on the media properties themselves. In particular, it is shown that for a general hyperbolic system of two equations in one space dimension, the solution is not periodic. Moreover, this can remain true even if the media gradients are assumed small. However, if the media gradients vanish, or if they vanish except for a bounded region of space, the solution is shown to be periodic for a large enough time. Furthermore, if these gradients vanish asymptotically at large distances, then the disturbances will be asymptotically periodic for increasing time. Special attention is given to the propagation of infinitesimal pressure disturbances through non-uniform steady flows of a lossless fluid.     

Density of localized states and linear specific heat for anderson model of amorphous semiconductors

The Anderson model is used to describe the role of electron correlation in localized states in amorphous semiconductors. We adopt a quasiparticle approach and discuss both the Fermi level pinning and the linear specific heat in terms of temperature and concentration changes of the one-particle density of states.Dedicated to Professor Miroslav Trlifaj on the occasion of his sixtieth birthday.     

On the synchronization of chains of nonlinear pendula connected by linear springs

In this work the theoretical model of multidimensional physical systems, representable as chains of nonlinearly coupled chaotic pendula subjected to harmonic excitations, is formulated and its nonlinear dynamics and synchronization characteristics are studied by means of a numerical approach. Some considerations on the role of the main system parameters are drawn. Dynamic perturbations, due for example to background interactions or to intrinsic pathological imperfections of the chain, are also taken into account. Their effect is analyzed with reference to two distinct situations: uniform application to all the pendula and localized application to the extremities of the chain.