Experimentally, the parabolic negat

Experimentally, the parabolic negative magnetoresistance associated with electron-electron interactions was first identified by Paalanen et al.137 in high-mobility GaAs-AlGaAs heterostructure channels. A more detailed study was made by Choi et al.55 In that paper, as well as in Ref.113, it was found that the parabolic magnetoresistance was less pronounced in narrow channels thanin wider ones. Choi et al. attributed this suppression to specular boundary scattering. It should be noted, however, that specular boundary scattering has no effect at all on the classical conductivity tensor σ0 (in the scattering time approximation; cf. Section II.A.2). Since the parabolic magnetoresistance results from the (ωcτ)2 term in 1/σ0xx [see Eq. (2.54)], one would expect that specular boundary scattering does not suppress the parabolic magnetoresistance (assuming that the result δσxy = δσyx = 0 still holds in the pure metal regimel > W). Diffuse boundary scattering does affect σ0, but only for relatively weak fields such that 2lcycl >∼ W (see Section II.A); hence, diffuse boundary scattering seems equally inadequate in explaining the observations. In the absence of a theory for electron-electron interaction effects in the pure metal regime, this issue remains unsettled.