Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 4: Quantenflüssigkeiten, Bose-Einstein Kondensate, ultrakalte Atome, ...
TT 4.7: Vortrag
Montag, 8. März 2004, 11:45–12:00, H19
Audio Demonstration of Quantum Oscillations: Phase Locking of Josephson Oscillations in superfluid 3He-B — •S.V. Pereverzev and G. Eska — Physikalisches Institut, Universität Bayreuth
We report on a family of dynamic effects which were observed in superfluid 3He flow through a weak link (array of 65x65 holes of 150 nm dia. in a 50 nm SiN membrane). The flow was driven by a time dependent pressure difference (Δ p(t)) to which an ac-modulation (pac cos(ω t + θ)) was added. A self-trapping phase-locked state could be observed when the Josephson frequency (ωJ (t) = Δ p(t)/ρ κ0) and the ac-drive frequency ω merged (reverse AC-Josephson effect). This trapped state is a zero net current state with a nonzero pressure difference across the weak link. Close to this resonance the observed beat frequency ωJ−ω clearly indicates the presence of Josephson oscillations which can be heared. Low frequency oscillations around this quasi-equilibrium state were also observed, as well as Helmholtz oscillations around the zero pressure-difference equilibrium state. The frequencies of both of these oscillatory modes depended on amplitude and frequency of the ac-drive. For the pressure driven flow we measured unexpected high losses. The origin of these losses is unclear.