The transition to superfluidity of 3 He in high porosity (98.2%) aerogel has been observed by nuclear magnetic resonance techniques. The onset of the transition at all pressures above 13 bar is marked by a sharp increase in NMR frequency similar to that observed in bulk 3 He-A. This suggests that the aerogel/superfluid phase is highly homogeneous although both the transition temperature, T c , and the amplitude of the order parameter are substantially suppressed. The aerogel strands are ~ 50Å in diameter, much smaller than the superfluid coherence length. Consequently, we have attempted to interpret our observations as an impurity scattering problem. Based on our measurements of the magnetic field dependence of T c it appears that both magnetic and potential scattering play important roles where the magnetic scattering can be associated with solid 3 He on the aerogel surface. This is determined by isotopic exchange with 4 He, a process which appears to stabilize a new superfluid state similar to the bulk B-phase.
ASJC Scopus subject areas
- Physics and Astronomy(all)