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  4. Weyl sums and the Lyapunov exponent for the skew-shift Schrödinger cocycle
 
research report

Weyl sums and the Lyapunov exponent for the skew-shift Schrödinger cocycle

Han, Rui
•
Lemm, Marius  
•
Schlag, Wilhelm
June 30, 2018

We study the one-dimensional discrete Schrödinger operator with the skew-shift potential $2\lambda\cos\left(2\pi \left(\binom{j}{2} \omega+jy+x\right)\right)$. This potential is long conjectured to behave like a random one, i.e., it is expected to produce Anderson localization for arbitrarily small coupling constants $\lambda>0$. In this paper, we introduce a novel perturbative approach for studying the zero-energy Lyapunov exponent $L(\lambda)$ at small $\lambda$. Our main results establish that, to second order in perturbation theory, a natural upper bound on $L(\lambda)$ is fully consistent with $L(\lambda)$ being positive and satisfying the usual Figotin-Pastur type asymptotics $L(\lambda)\sim C\lambda^2$ as $\lambda\to 0$. The analogous quantity behaves completely differently in the Almost-Mathieu model, whose zero-energy Lyapunov exponent vanishes for $\lambda<1$. The main technical work consists in establishing good lower bounds on the exponential sums (quadratic Weyl sums) that appear in our perturbation series.

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Type
research report
Author(s)
Han, Rui
Lemm, Marius  
Schlag, Wilhelm
Date Issued

2018-06-30

Editorial or Peer reviewed

REVIEWED

Written at

OTHER

EPFL units
CAMP  
Available on Infoscience
October 1, 2020
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/172107
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