Transverse acoustic impedance of normal liquid ³He with ⁴He coating

We measured the transverse acoustic impedance of the normal liquid ³He at 16 MHz and 10 bar with and without ⁴He layers plated on a wall in the temperature range of 500 to 3 mK. The real component of the impedance gradually increased with cooling in the high-temperature hydrodynamic region and saturated in the low-temperature collisionless region. In the crossover region around 20 mK, the real component had a steep increase and the imaginary component was minimum. Overall change in the temperature dependence became smaller by ⁴He coating and we can obtain the specularity parameter S of the wall by fitting the temperature dependence of the experimental impedance to the theory.