Sharp $\frac12$-H\"older continuity of the Lyapunov exponent at the bottom of the spectrum for a class of Schr\"odinger cocycles

Abstract

We consider a similar type of scenario for the disappearance of uniform of hyperbolicity as in Bjerkl\"ov and Saprykina (2008, Nonlinearity 21), where it was proved that the minimum distance between invariant stable and unstable bundles has a linear power law dependence on parameters. In this scenario we prove that the Lyapunov exponent is sharp $\frac12$-H\"older continuous. In particular, we show that the Lyapunov exponent of Schr\"odinger cocycles with a potential having a unique non-degenerate minimum, is sharp $\frac12$-H\"older continuous below the lowest energy of the spectrum, in the large coupling regime.