Critical Sound Damping: When Does Scaling Hold?

Using the dynamic specific-heat theory, we show that exponent y, associated with high-frequency damping at a second order phase transition $(\delta \bar{\alpha}\sim w^{1+y})$, is frequency-dependent. This result indicates that the dynamic scaling-laws predicting that the $\delta \bar{\alpha}/\delta \bar{\alpha}_\infty$ ratio is a homogeneous function of variable w τ are never rigorously verified (τ is the critical relaxation time). This calculation, which allows the degree of departure from these laws to be determined, is applied to various experimental situations.