Coulomb drag in coupled quantum wells: effects of bandstructure and {\bf q}-dependent scattering*

We study the effects of non-parabolicity of the band-structure and wavevector-dependent scattering rates on the Coulomb drag in coupled quantum wells, using a theoretical formulation that takes these effects into account [K. Flensberg and B. Y.-K. Hu, Phys.~Rev.~B {\bf 52}, 14796(1995)]. We examine the conditions in which this formulation reduces to the result given by von Oppen {\it et al.} [F. von Oppen, S. Simon and A. Stern, Phys.~Rev.~Lett. {\bf 87}, 106803 (2001)], in which the effects of band-structure are included through the terms $d\hat{\sigma} _i/dn_i$, where $\hat\sigma$ is the (single-layer) conductivity tensor and $n$ is the (single-layer) density and $i$ is the layer index. The effect of scattering that is strongly wavevector-dependent will also be discussed.