Critical damping of first and second sound at a smectic A-nematic phase transition

Abstract

Starting from a generalized hydrodynamic theory the eigenmodes in the vicinity of a smectic A-nematic phase transition are derived. It is necessary to take account of the non-hydrodynamic motions of the smectic order parameter and the director which slow down at the phase transition. This leads to a special anisotropy of the critical damping of first and second sound which agrees with existing experimental results. The temperature dependence of the critical damping is discussed in comparison with recent experimental results on the critical viscosities