arXiv subjects

Hatem Najar

Publications and source records attributed to Hatem Najar.

6 recordsLinked to original sources

arXiv2013

Lifshitz tails for matrix-valued Anderson models

This paper is devoted to the study of Lifshitz tails for a continuous matrix-valued Anderson-type model $H_ω$ acting on $L^2(\R^d)\otimes \C^{D}$, for arbitrary $d\geq 1$ and $D\geq 1$. We prove that the integrated density of states of $H_ω$ has a Lifshitz behavior at the bottom of the spectrum. We obtain a Lifshitz exponent equal to $-d/2$ and this exponent is independent of $D$. It shows that the behaviour of the integrated density of states at the bottom of the spectrum of a quasi-d-dimensional Anderson model is the same as its behaviour for a d-dimensional Anderson model.

math-ph↗

arXiv2012

Lifshitz tails for a percolation model in the continuum

In this paper we study Lifshitz tails for continuous Laplacian in a continuous site percolation situation. By this we mean that we delete a random set $Γ_ω$ from $IR^d$ and consider the Dirichlet or Neumann Laplacian on $D=IR^d\setminusΓ_ω$. We prove that the integrated density of states exhibits Lifshitz behavior at the bottom of the spectrum when we consider Dirichlet boundary conditions, while when we consider Neumann boundary conditions, it is bounded from below by a van Hove behavior. The Lifshitz tails are proven independently of the percolation probability, whereas for the van Hove case we need some assumption on the volume of the sets taken out as well as on the percolation probability.

math-ph↗

arXiv2011

Spectral and localization properties of the Dirichlet wave guide with two concentric Neumann discs

Bound states of the Hamiltonian describing a quantum particle living on three dimensional straight strip of width $d$ are investigated. We impose the Neumann boundary condition on the two concentric windows of the radii $a$ and $ b$ located on the opposite walls and the Dirichlet boundary condition on the remaining part of the boundary of the strip. We prove that such a system exhibits discrete eigenvalues below the essential spectrum for any $a,b>0$. When $a$ and $b$ tend to the infinity, the asymptotic of the eigenvalue is derived. A comparative analysis with the one-window case reveals that due to the additional possibility of the regulating energy spectrum the anticrossing structure builds up as a function of the inner radius with its sharpness increasing for the larger outer radius. Mathematical and physical interpretation of the obtained results is presented; namely, it is derived that the anticrossings are accompanied by the drastic changes of the wave function localization. Parallels are drawn to the other structures exhibiting similar phenomena; in particular, it is proved that, contrary to the two-dimensional geometry, at the critical Neumann radii true bound states exist.

math-ph↗

arXiv2005

The spectrum minimum for random Schrödinger operators with indefinite sign potentials

This paper sets out to study the spectral minimum for operator belonging to the family of random Schrödinger operators of the form $H\_{λ,ω}=-Δ+W\_{\text{per}}+λV\_ω$, where we suppose that $V\_ω$ is of Anderson type and the single site is assumed to be with an indefinite sign. Under some assumptions we prove that there exists $λ\_0>0$ such that for any $λ\in [0,λ\_0]$, the minimum of the spectrum of $H\_{λ,ω}$ is obtained by a given realization of the random variables.

math.SP↗

arXiv2005

Results dealing with the behavior of the integrated density of states of random divergence operators

In this paper we generalize and improve results proven for acoustic operators in \cite{jmp,long}. It deals with the behavior of the integrated density of states of random divergence operators of the form $H\_ω=\sum\_{i,j=1}^d\partial\_{x\_{i}}a\_{i,j}(ω,x)\partial\_{x\_j}$ ; on the internal band edges of the spectrum. We propose an application of such a result to get localization.

math.SP↗

arXiv2004

About a result of S.M. Kozlov

We give an alternative proof and improve upon a result of S.M. Kozlov \cite{ko}. It deals with the asymptotic of the integrated density of states of the acoustic operator $\displaystyle H_ω=-\nablaρ_ω\nabla$, at the bottom of the spectrum.

math-ph↗