Is the Behavior of Ultrasonic Absorption at Frequencies above 2 MHz in the Smectic-$A$ Phase of Terephthal-$\mathrm{bis}$-$p$-$p^{\prime }$-Butylaniline an Example of the Breakdown of Conventional Hydrodynamics?

This paper gives measurements of frequency-dependent ultrasonic damping, $\alpha$, at frequencies, $f$, between 2 and 21 MHz in the smectic-$A$ phase of terephthal-$\mathrm{bis}$-$p$-$p^{\prime }$-butylaniline. There is no trace of the considerable increase in $\frac{\alpha }{f^2}$ between 2 and 10 MHz reported by Bhattacharya and Ketterson, working on the same compound with a similar pulse technique. Our results question the existence of anharmonic effects within the frequency range investigated.