Journal of the European Mathematical Society

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Volume 14, Issue 1, 2012, pp. 61–106
DOI: 10.4171/JEMS/296

Opening gaps in the spectrum of strictly ergodic Schrödinger operators

Artur Avila[1], Jairo Bochi[2] and David Damanik[3]

(1) Université Pierre et Marie Curie, Paris, France
(2) PUC-Rio, Rio de Janeiro, Brazil
(3) Rice University, Houston, United States

We consider Schr¨odinger operators with dynamically defined potentials arising from continuous sampling along orbits of strictly ergodic transformations. The Gap Labeling Theorem states that the possible gaps in the spectrum can be canonically labelled by an at most countable set defined purely in terms of the dynamics. Which labels actually appear depends on the choice of the sampling function; the missing labels are said to correspond to collapsed gaps. Here we show that for any collapsed gap, the sampling function may be continuously deformed so that the gap immediately opens. As a corollary, we conclude that for generic sampling functions, all gaps are open. The proof is based on the analysis of continuous SL(2,$\mathbb R$) cocycles, for which we obtain dynamical results of independent interest.

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Avila Artur, Bochi Jairo, Damanik David: Opening gaps in the spectrum of strictly ergodic Schrödinger operators. J. Eur. Math. Soc. 14 (2012), 61-106. doi: 10.4171/JEMS/296