Sound Propagation in SuperfluidHe3near the Polycritical Point

Abstract

We report studies of 20-MHz sound propagation in the A and B phases above the polycritical point, and in the B phase below the polycritical point. Some striking features are observed which were not seen heretofore.The propagation of ultrasound is a powerful probe of the low-temperature superfluid phases of 3 He. 1 Earlier studies of sound propagation along the melting curve 2 and at lower pressures 3 showed a large peak in the attenuation at the normal-superfluid transition accompanied by a sharp, but monotonic, decrease in the sound velocity 3 which appeared to extrapolate to the hydrodynamic first-sound value at still lower temperatures. Sound propagation at the B-A transition has not been studied before at pressures between the polycritical point (PCP) and the melting curve; the phase diagram was established by different experimental probes. 1 ' 4 In this Letter we report the observation of (1) a discontinuity in both the velocity, c, and attenuation, a, at the B-A transition for pressures well above the PCP; (2) a change in slope of the temperature dependence of the velocity just above and below the discontinuity at the B-A transition for pressures just above the PCP; and (3) a change in slope of the temperature dependence of the velocity (suggestive of a divergence with a sign reversal) just above and below the attenuation peak which occurs below the B -to-normal 711 liquid transition at pressures below the PCP.Our measurements were performed in an epoxy adiabatic-demagnetization cell. The cell was precooled through a specially designed mechanical heat switch by the epoxy mixing chamber of our 3 He-4 He dilution refrigerator. The cell and heat switch are described in detail elsewhere. 5 The heat switch was actuated by a bellows which could be expanded (switch closed) using pressurized liquid 4 He. The demagnetization cell contained 23.2 g of cerium magnesium nitrate (CMN) together with a measured volume of 2.4 cm 3 of 3 He (including the sonic chamber). The sonic components were contained in an epoxy plug which was screwed into the bottom of the demagnetization cell; the threads were sealed with Nonaq stopcock grease. The sound path was defined by an 0 o 6-cm-long fused quartz annulus with an outside diameter of 1.27 cm and an inside diameter of 0.95 cm; the diameter of the sound path was further reduced to 0.6 cm by an epoxy annulus of nearly the same length in order to reduce the volume of 3 He in the cell. The ends of the quartz spacer were castellated (to minimize spurious transmission through the spacer and to

Zero-sound studies in superfluid 3He

“…5. Although our data are more scattered than those of Roach et al, 11 we were able to follow the 15-MHz signal through the attenuation peak, centered at 1 -T/T~ = 0.0042, thereby observing structure in the temperature region inaccessible to the Argonne group, who worked at 20 MHz. Instead of a sharp divergence and sign-reversal-type behavior at the collective modes peak, we see at best a very modest rise and then a smooth decrease to a lower velocity as the temperature is decreased.…”

“…38 In particular recent experiments have been valuable in confirming the anisotropy of excitation of collective modes in 3He-A9'l~ and the isotropy of excitation of collective modes in 3He-B. 11 This paper is based on new measurements made in zero magnetic field over a wide range of pressure at 5, 15, and 25 MHz in the temperature range near to T~.. After an exposition of experimental arrangement and technique we shall discuss our results on 3He-B; these include data on the size, shape, and location of the collective modes peak. We also deduce values of the strong coupling parameter, present some data on the velocity of sound, and show evidence for the existence of a pair-breaking peak.…”

Superfluid optomechanics: coupling of a superfluid to a superconducting condensate

“…Furthermore, fascinating experiments have recently been accomplished with small quantum condensates of atomic vapors coupled to optical resonators. [10,11] In light of this, superfluid 4 He, a condensate which can easily be prepared in macroscopic quantities and demonstrates frictionless motion at zerofrequency [12], is an intriguing material to consider for the study of quantized macroscopic motion [3] and quantized mechanical fields. [13] Acoustic dissipation of first sound of superfluid 4 He is a very well studied and understood process.…”