Crossover from hydrodynamic to acoustic drag on quartz tuning forks in normal and superfluid 4He

We present measurements of the drag forces on quartz tuning forks oscillating at low velocities in normal and superfluid 4He. We have investigated the dissipative drag over a wide range of frequencies, from 6.5 to 600 kHz, by using arrays of forks with varying prong lengths and by exciting the forks in their fundamental and first overtone modes. At low frequencies the behavior is dominated by laminar hydrodynamic drag, governed by the fluid viscosity. At higher frequencies acoustic drag is dominant and is described well by a three-dimensional model of sound emission

YbPd2In : A promising candidate for strong entropy accumulation at very low temperature

We report on synthesis, crystal structure, magnetic, thermodynamic, and transport properties of the compound YbPd2In, crystallizing as a Heusler structure type. A trivalent state of the rare earth was determined by fitting the magnetic susceptibility with a Curie-Weiss law. This compound is characterized by showing very weak magnetic interactions and a negligible Kondo effect. A specific-heat jump was observed at T 48250mK, followed at higher temperature by a power-law decrease of CP(T)/T. The resulting large electronic entropy increase at very low temperature is rapidly shifted to higher temperature by the application of magnetic field. This magnetocaloric effect places YbPd2In as a very good candidate for adiabatic demagnetization cooling processes

Probing Andreev reflection in superfluid He-3-B using a quartz tuning fork.

Direct measurements of the Andreev reflection of the quasiparticles excitations in superfluid He-3-B in the ballistic regime at 0.5 bar using a quartz tuning fork are presented. Based on these measurements, we were able to determine the value of the ratio Delta(0)/kT(c) to be 1.71, in reasonable agreement with previous measurements. Moreover, it seems that Andreev reflection of excitations gives a possibility to determine the value of the constant lambda characterizing the velocity field profile. This value for a tuning fork was estimated to be 1.28, different from that for cylindrical wire (lambda similar to 0.95), suggesting that the anti-phase oscillatory motion and the geometry of the tuning prongs lead to an enhancement of the velocity of the superfluid flow