Extended states in disordered systems: Role of off-diagonal correlations

We study one-dimensional systems with random diagonal disorder but off-diagonal short-range correlations imposed by structural constrains. We find that these correlations generate effective conduction channels for finite systems. At a certain golden correlation condition for the hopping amplitudes, we find an extended state for an infinite system. Our model has important implications to charge transport in DNA molecules, and a possible set of experiments in semiconductor superlattices is proposed to verify our most interesting theoretical predictions.