COEFFICIENTS OF THE 2ND VISCOSITY IN THIN LIQUID-HELIUM FILMS

The coefficients of the second viscosity in thin liquid-helium films are evaluated explicitly as a function of temperature (T) via interactions between elementary excitations that include the anomalous excitation spectrum. For T greater-than-or-similar-to 0.3 K the coefficients behave like those of the bulk liquid helium, while for T less-than-or-similar-to 0.3 K the temperature variations of four coefficients of the second viscosity show a T-1 dependence, which is due to the three-phonon processes (3PP) originating from the anomalous excitation spectrum of two-dimensional liquid helium at low momenta and low temperatures. The T-1 dependence also appears in the first viscosity of bulk and thin liquid helium, which is based on the 3PP.