EXTENDED AND LOCALIZED STATES OF GENERALIZED KICKED HARPER MODELS

Basic properties of quantum states for generalized kicked Harper models are studied using the phase-space translational symmetry of the problem. Explicit expressions of the quasienergy (QE) states are derived for general rational values q/p of a dimensionless HBAR. The quasienergies form p bands and the QE states are q-fold degenerate. With each band one can associate a pair of integers sigma and mu determined from the periodicity conditions of the QE states in the band. For q = 1, sigma is exactly the Chern index introduced by Leboeuf et al. [Phys. Rev. Lett. 65, 3076 (1990)] for a characterization of the classical-quantum correspondence. It is shown, however, that sigma is always different from zero for q > 1. The Chern-index characterization is then generalized by introducing localized quantum states associated in a natural way with sigma = 0. These states are formed from q QE bands with a total sigma = 0 and they define q equivalent new bands, each with sigma = 0. While these states are nonstationary, they become stationary in the semiclassical limit p --> infinity.