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Abel Klein

Publications and source records attributed to Abel Klein.

44 records · Page 3Linked to original sources

Persistence of Anderson localization in Schrödinger operators with decaying random potentials

We show persistence of both Anderson and dynamical localization in Schrödinger operators with non-positive (attractive) random decaying potential. We consider an Anderson-type Schrödinger operator with a non-positive ergodic random potential, and multiply the random potential by a decaying envelope function. If the envelope function decays slower than $|x|^{-2}$ at infinity, we prove that the operator has infinitely many eigenvalues below zero. For envelopes decaying as $|x|^{-α}$ at infinity, we determine the number of bound states below a given energy $E<0$, asymptotically as $α\downarrow 0$. To show that bound states located at the bottom of the spectrum are related to the phenomenon of Anderson localization in the corresponding ergodic model, we prove: (a) these states are exponentially localized with a localization length that is uniform in the decay exponent $α$; (b)~ dynamical localization holds uniformly in $α$.

math-ph↗

On Mott's formula for the ac-conductivity in the Anderson model

We study the ac-conductivity in linear response theory in the general framework of ergodic magnetic Schrödinger operators. For the Anderson model, if the Fermi energy lies in the localization regime, we prove that the ac-conductivity is bounded by $C ν^2 (\log \frac 1 ν)^{d+2}$ at small frequencies $ν$. This is to be compared to Mott's formula, which predicts the leading term to be $C ν^2 (\log \frac 1 ν)^{d+1}$.

math-ph↗

On localization for the Schrödinger operator with a Poisson random potential

We prove exponential localization for the Schrödinger operator with a Poisson random potential at the bottom of the spectrum in any dimension. We also prove exponential localization in a prescribed interval for all large Poisson densities. In addition, we obtain dynamical localization and finite multiplicity of the eigenvalues.

math-ph↗

New characterizations of the region of complete localization for random Schrödinger operators

We study the region of complete localization in a class of random operators which includes random Schrödinger operators with Anderson-type potentials and classical wave operators in random media, as well as the Anderson tight-binding model. We establish new characterizations or criteria for this region of complete localization, given either by the decay of eigenfunction correlations or by the decay of Fermi projections. (These are necessary and sufficient conditions for the random operator to exhibit complete localization in this energy region.) Using the first type of characterization we prove that in the region of complete localization the random operator has eigenvalues with finite multiplicity.

math-ph↗

Linear response theory for magnetic Schroedinger operators in disordered media

We justify the linear response theory for an ergodic Schroedinger operator with magnetic field within the non-interacting particle approximation, and derive a Kubo formula for the electric conductivity tensor. To achieve that, we construct suitable normed spaces of measurable covariant operators where the Liouville equation can be solved uniquely. If the Fermi level falls into a region of localization, we recover the well-known Kubo-Streda formula for the quantum Hall conductivity at zero temperature.

math-ph↗

Dynamical delocalization in random Landau Hamiltonians

We prove the existence of dynamical delocalization for random Landau Hamiltonians near each Landau level. Since typically there is dynamical localization at the edges of each disordered-broadened Landau band, this implies the existence of at least one dynamical mobility edge at each Landau band, namely a boundary point between the localization and delocalization regimes, which we prove to converge to the corresponding Landau level as either the magnetic field or the disorder goes to zero.

math-ph↗