Frequency-dependent ultrasound attenuation in superfluid H 3 e in aerogel

Ultrasound attenuation measurements in the $B$-like phase of superfluid $^{3}\text{H}\text{e}$ embedded in 98% porosity aerogel have been performed at four frequencies between 3.6 and 11.3 MHz. At all of the pressures studied (14, 25, and 33 bar), the attenuation exhibits nontrivial frequency dependences that progressively deviate from the hydrodynamic ${\ensuremath{\omega}}^{2}$ behavior as the temperature decreases. This behavior is related to the structure of the impurity states inside the gap and could offer a tool to profile the gap structure in this system.