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Neutron reflection from the surfaces of liquid 4He and a dilute 3He-4He Solution.

Research output: Contribution to journalJournal article


Article number032022
<mark>Journal publication date</mark>2009
<mark>Journal</mark>Journal of Physics: Conference Series
Number of pages4
<mark>Original language</mark>English


Conference25th International Conference on Low Temperature Physics (LT25)


We report and discuss the first neutron reflection measurements from the free surfaces of normal and superfluid 4He and of a liquid 3He-4He mixture. In case of liquid 4He the surface roughness is different above and below the lambda transition, being smoother in the superfluid state. For the superfluid, we also observe the formation of a surface layer ~ 200 Å thick which has a subtly different neutron scattering cross-section. The results can be interpreted as an enhancement of the Bose-Einstein condensate fraction close to the helium surface. We find that the addition of 3He isotopic impurities leads to the formation of Andreev levels at low temperatures.