Second Sound inHe3-He4Mixtures below 1°K

Abstract

An investigation has been made of second sound in mixtures of He 3 -He 4 in the temperature region obtained by demagnetization of a paramagnetic salt. Several concentrations of He 3 were used ranging between 0.0017 percent and 4.3 percent. The velocity of second sound for the mixtures was found to reach a maximum value of about 35 meters/sec just below 1°K and to approach 20 meters/sec near 0.2°K. In addition, essentially no dispersion of second-sound pulses in mixture below 1°K was observed. This is in marked contrast to heat pulses in pure He 4 in this temperature region. Our results show general agreement with the theoretical predictions of Pomeranchuk, provided the effective mass ju of the He 3 atom is allowed to vary from 2.0 m 3 at 0.2°K to 3.6 m 3 at 1.8°K. * Assisted by the U. S. Office of Naval Research.

Decoupling between first sound and second sound in $^3$He - superfluid $^4$He mixtures

“…The velocity of second sound ranges approximately between 0 m/s and 40 m/s, in the temperature and concentration range of our experiment. Largest values are obtained at low temperatures and at high concentrations, while near T λ it tends to zero, as second sound ceases to exist 8,[23][24][25][26] . Since the second sound velocity has a significant temperature and concentration dependence, there exist numerous possible standing sound wave modes that can be observed with a quartz tuning fork 27 .…”

Decoupling of first sound from second sound in dilute He3–superfluidHe4 mixtures

“…The velocity of second sound ranges approximately between 0 and 40 m/s in the temperature and concentration range of our experiment. Largest values are obtained at low temperatures and at high concentrations, while near T λ it tends to zero, as second sound ceases to exist [9,[24][25][26][27]. Since the second sound velocity has a significant temperature and concentration dependence, there exist numerous possible standing sound wave modes that can be observed with a quartz tuning fork [28].…”