  We study potential scattering in a two-dimensional electron gas with Rashba
spin-orbit coupling in the limit that the energy of the scattering electron
approaches the bottom of the lower spin-split band. Focusing on two
spin-independent circularly symmetric potentials, an infinite barrier and a
delta-function shell, we show that scattering in this limit is qualitatively
different from both scattering in the higher spin-split band and scattering of
electrons without spin-orbit coupling. The scattering matrix is purely
off-diagonal with both off-diagonal elements equal to one, and all angular
momentum channels contribute equally; the differential cross section becomes
increasingly peaked in the forward and backward scattering directions; the
total cross section exhibits quantized plateaus. These features are independent
of the details of the scattering potentials, and we conjecture them to be
universal. Our results suggest that Rashba scattering in the low-energy limit
becomes effectively one-dimensional.
