Finite-frequency transport of composite fermions

We study the AC properties of a two-dimensional electron gas in high-mobili ty samples at half-filling of the lowest Landau level within the framework of the composite-fermion (CF) theory. We have shown that the low-frequency behavior of the AC conductivity sigma (xx)(omega) in the presence of smooth disorder is governed by quasiclassical memory effects that are related to return processes neglected in Boltzmann transport theory. We have demonstra ted that the fictitious random magnetic field acting on CFs strongly enhanc es this anomalous contribution to sigma (xx)(omega); specifically, the retu rn-induced correction to Re sigma (xx)(omega) shows a pronounced cusp propo rtional to/omega/ . This anomaly is of quasiclassical origin and dominates (compared to quantum corrections proportional to ln omega) in a wide freque ncy range, provided k(F)d much greater than 1, where k(F) is the CF Fermi w ave vector, d the correlation radius of disorder. The prefactor of the /ome ga/ term is proportional to d/l (l is the mean free path of the CFs). (C) 2 001 Elsevier Science B.V. All rights reserved.