Periodic structure and Schrodinger operators for codings of circle rotations

Abstract

We consider, for any irrational $\alpha$ and interval $I\subset \mathbb{T}$, the 2-interval coding subshift $X^{(I,\alpha )}$ induced by coding orbits under repeated rotation by $\alpha$ via membership in $I$ or $I^c$. Each sequence $c\in X^{(I,\alpha )}$ has an associated Schrödinger operator $H_c$, and in \cite{kaminaga} it was proved that if the continued fraction of $\alpha$ has digits with limsup at least $4$, then almost every $c\in X^{(I,\alpha )}$ has so-called $3$-block Gordon structure, which implies that the operator $H_c$ has no eigenvalues. We significantly improve this result by completely characterizing almost-sure $3$-block Gordon structure, proving that in fact it holds for all $(\alpha ,I)$ except for a countable set of pairs $(\alpha ,|I|)$ where $\alpha$ is Möbius equivalent to the silver mean and $|I|\in \mathbb{Z}\alpha +f(\alpha )$ where $f(\alpha )$ is a specific infinite series taking value either $\frac{1}{2},\frac{\alpha }{2}$, or $\frac{\alpha +1}{2}$. We also show that for a set of $\alpha$ of full measure, and for every $I$, the set of points whose orbit codings do not have $3$-block Gordon structure has Hausdorff dimension bounded away from $1$.

23 pages