Localization in an Almost Periodically Modulated Array of Potential Barriers

It is argued that an array of potential barriers modulated in position and strength in a manner incommensurate with the barrier spacing can be replaced by a $\delta$-function Kronig-Penny model. With this equivalence it is shown, with use of renormalization-group arguments as well as known results from other calculations, that this model possesses both localized and extended states separated by mobility edges.