QFS2016 Book of Abstracts

Abstracts

P4.12 Sub-superfluid 3-He coherence length cross-section SiNN (Silicon Nitride – Niobium) wires. De Alba, R(1), Abhilash T.S(1), Rand R.(2) and Parpia, J.M.(1) 1) Department of Physics, Clark Hall, Cornell University, Ithaca NY 14850 USA 2) Department of Mathematics, Malott Hall, Cornell University, Ithaca NY 14850 USA We report on the room temperature characterization of ultrafine composite wires formed of high stress Silicon Nitride onto which a film of superconducting Nb was evaporated. The wires’ cross section (50 nm square) is less than the coherence length of superfluid 3 He. We describe the fabrication details of the wires, together with room temperature characterization of the resonant frequency and Q of the wires with and without the additional Nb layer. Further we will describe the so-called “self oscillation regime” where these devices execute harmonic motion when illuminated with intense laser light. We observe stable limit-cycle behavior with an amplitude of roughly one-eighth of the impinging laser wavelength, and characterize entrainment of this motion with inertial forcing. Such parametric drive implemented with double-frequency driving force may enable these devices to be operated in the viscous as well as ballistic regimes in norml and superfluid 3 He. P4.13 The influence of high magnetic field on resonant characteristics of high Q-value quartz tuning fork in vacuum in milikelvin temperature range ˇCloveˇcko Marcel, Kupka Martin, Skyba Peter, Vavrek Frantiˇsek Centre of Low Temperature Physics, Institute of Experimental Physics, SAS and P. J. ˇSaf´arik University Koˇsice, Watsonova 47, 04001 Koˇsice, Slovakia We have extensively studied the influence of high magnetic field (up to 8 Tesla) on vacuum resonant characteristics of a commercially available 32 kHz quartz tuning fork in millikelvin temperature range. High magnetic field applied perpendicularly to both the direction of oscillations and piezoelectric current generates additional force acting on oscillating electric dipoles inside quartz. This additional force (as a possible source of de-coherence) effectively stiffens the quartz crystal manifested by the rise of resonance frequency and simultaneously decreases its electrical conductivity which leads to additional dissipation. We discuss a physical origin of the observed phenomenon.

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