Second Sound in Solids at Low Temperature

The phenomenon of second sound in liquid He II was first predicted in the theoretical works of Tisza [78] and Landau [79]. Later Peshkov [80] detected this wave and confirmed that its temperature variations are uncoupled from the pressure variations: therefore the second sound is often referred to as a temperature wave. This phenomenon is now well understood. We described it in Chapter 3 following the work of Dreyer [81], who showed that the bifluid theory of Tisza and Landau is a special case of the thermodynamic theory of binary mixtures in general.