Semiclassical transport in a random magnetic field

We present a theoretical description of the semiclassical kinetics of two-dimensional fermions in a smoothly varying random magnetic field (RMF), with emphasis on the composite-fermion (CF) approach to the half-filled Landau level. We demonstrate that the Drude picture of the CF kinetics is only marginally valid at v = 1/2 and becomes totally inadequate already at a small deviation from half-filling. We show that the non-Markovian character of the transport leads to a strong positive magnetoresistance rho(xx) at small v - 1/2. At larger deviations from v = 1/2, the positive magnetoresistance is followed by a sharp falloff of rho(xx) ("adiabatic localization"). We show that the AC conductivity sigma(xx)(omega) in the long-range RMF exhibits distinct non-Drude features. In particular, it has a sharp kink [sigma(xx)(omega) - sigma(xx)(0) proportional to \omega\] at zero omega and falls off exponentially at higher omega. (C) 2000 Elsevier Science B.V. All rights reserved.