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We study the localization properties of disordered one-dimensional tight-binding lattices driven by ac fields. The localization length of the electrons increases when the frequency of the driving field is smaller than the bandwidth. We show that there is an optimal value of the amplitude of the driving field for which the localization length of the system is maximal. This maximum localization length increases with the inverse of the driving frequency. Real materials always contain a certain degree of disorder since the atomic structure is never perfectly regular. In fact, many physical properties are either influenced or even mainly determined by this randomness. The understanding of the effects of disorder in the physical properties of a material is therefore of great practical importance and has played a central role in condensed matter physics in the last half century. 1One of the most simple disordered systems is the motion of a particle in a one-dimensional ͑1D͒ random potential. Realizations of this system can be studied experimentally, e.g., in semiconductor superlattices ͑SL͒ in the coherent regime.2 If the system is long enough its eigenstates are exponentially localized due to disorder. Electrons in these localized states are spatially confined and their only contribution to transport is through thermally activated hopping. The main quantity of interest in this case is the localization length of the electron wave functions, which is controlled by the ratio between the bandwidth ⌬ and the strength of the disorder W. A disordered system of length L Ͼ will behave as an insulator while a system with length L Ͻ will behave as a conductor.

We derive an exact expression for the transmission amplitude of a particle moving through a harmonically driven delta-function potential by using the method of continued-fractions within the framework of Floquet theory. We prove that the transmission through this potential as a function of the incident energy presents at most two real zeros, that its poles occur at energies nhω + ε * (0 < Re(ε * )

We calculate the dc conductance at zero temperature of clean quantum wires driven by a laser field. In the high-frequency regime we find an interplay between length-dependent interference effects and dynamical localization, which leads to a modulation by a Bessel function of the even-odd oscillations in the conductance. In the low-frequency regime we find that the field suppresses these oscillations. We present some analytical expressions for each of these frequency limits.