Photoconductivity in AC-driven modulated two-dimensional electron gas in aperpendicular magnetic field

Abstract

In this work we study the microwave photoconductivity of a two-dimensionalelectron system (2DES) in the presence of a magnetic field and a two-dimensionalmodulation (2D). The model includes the microwave and Landau contributions ina non-perturbative exact way; the periodic potential is treated perturbatively.The Landau–Floquet states provide a convenient base with respect to which thelattice potential becomes time dependent, inducing transitions between theLandau–Floquet levels. Based on this formalism, we provide a Kubo-like formula thattakes into account the oscillatory Floquet structure of the problem. The totallongitudinal conductivity and resistivity exhibit strong oscillations, determined byϵ = ω/ωc, withω the radiationfrequency and ωc the cyclotron frequency. The oscillations follow a pattern with minima centredat , and maxima centred at , where j = 1,2,3...,δ∼1/5 is a constantshift and l is the dominant multipole contribution. Negative resistance states (NRSs) develop asthe electron mobility and the intensity of the microwave power are increased.These NRSs appear in a narrow window region of values of the lattice parameter(a),around a∼lB, where lB is the magnetic length. It is proposed that these phenomena may be observed inartificially fabricated arrays of periodic scatterers at the interface of ultracleanGaAs /AlxGa1−xAs heterostructures.