Fluid slip at walls with mesoscopic surface roughness

The traditional picture of fluid slip at boundaries as a manifestation of a mean free path effect has to be revised whenever the boundary acquires a finite curvature on mesoscopic length scales. A finite boundary curvature gives rise to additional quasiparticle backscattering events, which enhance the transfer of transverse momentum to the surface with respect to the case of purely diffuse scattering off a flat surface. As a consequence, the experimentally determined effective slip length is reduced below its value for diffusely scattering flat surfaces. We discuss this new effect on the level of phenomenological hydrodynamic theory using a simple model for mesoscopic surface roughness. Our results explain discrepancies between experimentally observed fluid flow and conventional slip theory.