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Etude des ondes de spin dans le mélange 3He-4He liquide polarisé

Abstract : The exchange interaction in degenerate liquid 3He is at the origin of coherent effects like spin waves or the Leggett-Rice effect. At low polarisation these effects are well described by the Leggett equations and they are only visible at low temperature and in sufficiently high
magnetic fields. The question is if at high polarisation the phase space between “up” and “down” Fermi levels is available for collisions damping the spin coherence even at zero temperature. In this case the collision time for these effects varies like 1/(T2+TA2) where TA is
proportional to the polarisation and induces dissipation at T = 0 K. The existence of this dissipation has been subject of a theoretical and experimental debate. Until now, only the Leggett-Rice effect data by Akimoto et al. giving TA/B ~ 0.28 mK/Tesla agree with a theoretical prediction. Our data falls in the temperature range 10-30 mK but we are able to enhance polarisation by more than a factor 3 with respect to its equilibrium value (an effective field of more than 34 Tesla). We measure TA/Beff ~ 0,3 mK/Tesla, a value compatible with the
same theoretical model.
The calibration of our vibrating wire viscometers versus temperature resulted in a surprising effect. Below 100 mK and for all our wires (diameters between 25 and 115 μm), the 3He-4He mixtures behave like a normal liquid in the bulk, but like a superfluid on the surface: the momentum transfer parallel to the interface between the wire and the liquid almost vanishes. The departure from hydrodynamic behaviour is parametrised by a slip length, usually of the order of the mean free path. We have seen an enhancement of this length by a factor 1000 due to the presence of a superfuid 4He film on the walls. Below 10 mK, when the mean free path becomes of order of the wire diameter we also observe slip perpendicular to the surface of the wire. The microscopic model of Bowley and Owers-Bradley agrees very well with our measurements and allows us to extract the viscosity of the mixture, which we convert into temperature for the spin waves measurement.
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https://tel.archives-ouvertes.fr/tel-00113557
Contributor : Sorin-Mihai Perisanu <>
Submitted on : Monday, November 13, 2006 - 5:31:08 PM
Last modification on : Friday, December 18, 2020 - 1:34:03 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 7:03:01 PM

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  • HAL Id : tel-00113557, version 1

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Sorin-Mihai Perisanu. Etude des ondes de spin dans le mélange 3He-4He liquide polarisé. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 2005. Français. ⟨tel-00113557⟩

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