  Unexpected transport behavior can arise due to anisotropic single-particle
scattering in multiband systems. Specifically, we show within a semiclassical
Boltzmann approach beyond the relaxation-time approximation that anisotropic
scattering between electronlike and holelike Fermi surfaces generically leads
to negative transport times, which in turn cause negative magnetoresistance, an
extremum in the Hall coefficient, and a reduction of the resistivity. The
anisotropy required for this to occur decreases with increasing mismatch
between the Fermi-surface radii.
