Capillary waves at the transition from propagating to overdamped behavior -: art. no. 096104

We measure the dispersion relation of capillary waves on a liquid surface by heterodyne x-ray photon correlation spectroscopy near the transition from propagating to overdamped dynamic behavior. A strong deviation of the propagation frequency from the small-damping result omega(p)proportional tok(3/2) is observed long before the actual transition where (partial derivativeomega(p)/partial derivativek)<0 and omega(p) tends to zero. This behavior is successfully described by expressions derived within linear response theory.