Measurements of the dynamic structure factor near the lambda temperature in liquid helium

摘要: The dynamic structure factor S (q, ..omega..) was measured by Brillouin scattering in liquid /sup 4/He at q = 1.79 x 10/sup 5/ cm/sup -1/. Results were obtained two densities: rho 0.175 g/cm/sup 3/ for which P/sub lambda/ 23.1 bars and 0.179 28.5 bar. Values of the reduced temperature epsilon equivalent (T-T/sub lambda/)/T/sub varied from -5 -2/ to -6/ 1.3 -5/ 5 -2/. This range involves both hydrodynamic critical regions; values qxi fall between 21 below T/sub 4.5 2 above lambda/. article presents data on mode, is second sound transition heat diffusion above. most striking result that damping mode essentially independent over entire temperatures studied. behavior qualitatively different strong dependence, consistent with scaling, observed low frequencies. On other hand, any dispersion velocity high frequency (approx.more » several MHz) sound, if present, less than 2%. retains a two-peaked well into region lambda/; it still appears spectra (which contain instrumental width as well) approx. 4. At just above, there evidence non-Lorentzian shape ..omega..). contribution compared theoretical calculation Hohenberg, Siggia, Halperin based planar-spin model 4/He. theory matches overall general features within our spectral resolution However, closer 1 region, regions lambda/, predicts linewidths are too small.« less