We study the van der Waals friction between two flat metal surfaces in relative motion. For good conductors, we find that normal relative motion gives a much larger friction than for parallel relative motion. The friction may increase by many orders of magnitude when the surfaces are covered by adsorbates, or can support low-frequency surface plasmons. In this case, the friction is determined by resonant photon tunneling between adsorbate vibrational modes, or surface plasmon modes.

• Received 1 May 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.106101