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

Abstract

Riekki, Tapio; Manninen, M. S.; Tuoriniemi, Juha Decoupling of first sound from second sound in dilute 3He-superfluid 4He mixtures Bulk superfluid helium supports two sound modes: first sound is an ordinary pressure wave, while second sound is a temperature wave, unique to superfluid systems. These sound modes do not usually exist independently, but rather variations in pressure are accompanied by variations in temperature, and vice versa. We studied the coupling between first and second sound in dilute 3 He -superfluid 4 He mixtures, between 1.6 and 2.2 K, at 3 He concentrations ranging from 0% to 11%, under saturated vapor pressure, using a quartz tuning fork oscillator. Second sound coupled to first sound can create anomalies in the resonance response of the fork, which disappear only at very specific temperatures and concentrations, where two terms governing the coupling cancel each other, and second sound and first sound become decoupled.

Effects of 4He Film on Quartz Tuning Forks in 3He at Ultra-low Temperatures

“…These influence the width (full width at half maximum) and the frequency of the fork resonance. The characteristic dimensions of a typical QTF may also match the wavelength of first or second sound in pure helium or isotope mixtures, at certain temperature and pressure, resulting in acoustic phenomena [5,6,7] that are interesting in their own right, but can also make interpreting the fork data more difficult.…”