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 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 ρxx at small . At larger deviations from , the positive magnetoresistance is followed by a sharp falloff of ρxx (“adiabatic localization”). We show that the AC conductivity σxx(ω) in the long-range RMF exhibits distinct non-Drude features. In particular, it has a sharp kink [σxx(ω)−σxx(0)∝|ω|] at zero ω and falls off exponentially at higher ω