Studies of superfluid ³He confined to a submicron slab geometry

• Main Author: Corcoles, Antonio
• Published: Royal Holloway, University of London 2006
• Subjects: 530.42
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427928

The phase diagram of superfluid 3He is predicted to be modified when confined to a regular geometry of size comparable to the superfluid coherence length. This thesis addresses the problem of the effect of such a small geometry on the order parameter of the superfluid. The samples are probed by two methods: Nuclear Magnetic Resonance and a Torsional Oscillator. Nuclear Magnetic Resonance provides information about the spin dynamics of the system. This information can be used to identify the superfluid phases. The damping and frequency change of the torsion pendulum determine the hydrodynamic response of the fluid and they can be used to identify superfluidity and measure the superfluid density. The bulk anisotropy of the superfluid density could potentially help to identify the A-phase, although information sufficient to unambiguously determine the particular superfluid phase from the torsional oscillator is probably not possible in our experiment. The NMR experiment involved the construction of a high sensitivity SQUID spectrometer which allowed the observation of samples of the order of 1 x 1017 spins. We observed superfluidity in a variety of samples. The superfluid phases were identified as A- and B-phases in small droplets distributed over the experimental cell. These droplets were formed due to imperfect annealing of the samples. For a 3 Jlm thick slab we observed a strongly supercooled A-phase at temperatures as low as f-)0.38 mK. This A-phase suddenly underwent a transition into B-phase after a period of ",,20 hours independently of the temperature to which it had been supercooled. With the torsional oscillator we could see superfluidity in a film of nominal thickness of 143 nm. The dependence of the superfluid density on temperature agreed with most of the previous work, theoretical and experimental alike. It also showed remarkable similarities with other disordered systems like superfluid 3He in aerogel, although these similarities were not quantitative