  Two-dimensional systems with Rashba spin-orbit coupling are not Galilean
invariant and therefore electron--electron collisions in them may affect the
current. However when taken alone, they cannot ensure a nonzero dc resistivity,
so their effects are masked by impurity scattering. Here we calculate the
related finite-frequency response and show that the electron--electron
scattering in clean Rashba conductors decreases the Drude weight while
resulting in a finite dissipative component of the response outside of the
Drude peak.
