We analyze interference between bulk and boundary scattering channels in ultrathin metal films with rough surfaces in quantum-size-effect conditions. We identify two different sources of such interference. The first, which we call the mixing interference, is associated with inversion of collision operator with surface and bulk scattering terms. This inversion always leads to mixing of bulk and surface terms, even if the scattering channels are formally independent, as long as the collision operator does not have a $\delta$-type structure (the relaxation time approximation). The second source of interference, or what we called the intrinsic interference, is associated with the physical entanglement of the scattering processes and the fact that these processes are never really independent unless both are described by the Born approximation. The intrinsic interference dominates in low-temperature clean films or when the correlation radius of surface roughness is large. The mixing interference dominates in films with robust impurity and surface scattering.

• Received 11 June 2011

DOI:https://doi.org/10.1103/PhysRevB.84.165432