EXTENDED STATES IN ONE-DIMENSIONAL RANDOM-SEGMENT MODELS

We study here some one-dimensional (1D) disordered tight-binding models which can be constructed by randomly inserting a number of identical segments into an infinite purely periodic chain. We analytically show that under certain conditions there exist some completely unscattered states whose number is one less than the number of sites in each segment. The energies of these states are exactly determined. Some 1D models with random periods can be considered as samples of the random-segment models. The energy spectrum and unscattered wave functions of a sample model with different choices of parameters are illustrated.