A lower bound on the Lyapunov exponent for the generalized Harper's model
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abstract
We obtain a lower bound for the Lyapunov exponent of a family of discrete Schr"{o}dinger operators $(Hu)_n=u_{n+1}+u_{n-1}+2a_1cos2pi( heta+nalpha)u_n+2a_2cos4pi( heta+nalpha)u_n$, that incorporates both $a_1$ and $a_2,$ thus going beyond the Herman's bound.