Evidence for a Second Order B to A Phase Transition in Superfluid 3He in Low Density Silica Aerogels
Douglas D. Osheroff
Department of Physics, Stanford University, Stanford, CA 94305-4060, U.S.A.
CW-NMR studies of superfluid 3He in 99.4porosity silica aerogels show similar phase diagrams, with an equal spin pairing (ESP) A-like state stable near Tc, and a B-like phase stable at lower temperatures. On cooling through Tca, the sample magnetization and frequency shift show substantial supercooling, with discontinuous changes to B-like behavior seen at about 0.8 Tca. On warming, both the frequency shift and magnetization change continuously as the sample enters the ESP state, suggesting that this phase transition must be second order, with the components of the order parameter varying smoothly across the transition.
Pulsed NMR experiments in superfluid 3He confined in aerogel
Vladimir V. Dmitrieva, Ivan V. Kosareva, Norbert Muldersb, Vladislav V. Zavjalova, Dmitry Ye. Zmeeva
aKapitza Institute, Kosygina Str. 2, Moscow, 117334, Russia
bDepartment of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 USA
We have performed pulsed NMR experiments in both B- and overcooled A-like phases of superfluid 3He confined within 98% aerogel. The tipping angle dependencies of spin precession frequency in B-like phase of superfluid 3He in aerogel are found to be quite different for the case of pure 3He and for the cell preplated with 4He. The most interesting result of the experiment with 4He preplated aerogel is the observation of a sharp increase of the frequency shift for the tipping angles greater than 104° as it expected to be for the B-phase structure of the order parameter. The dependence of the frequency versus the tipping angle in overcooled A-like phase is similar for both pure and 4He preplated aerogel.
Viscoelastic theory of liquid 3He in aerogel
Seiji Higashitani, Takayuki Ichikawa, Mikio Yamamoto, Masaki Miura, Katsuhiko Nagai
Faculty of Integrated Arts and Sciences, Hiroshima University, Kagamiyama 1-7-1, Higashi-Hiroshima 739-8521, Japan
The impurity scattering effect on sound propagation properties of liquid 3He in aerogel is studied from the aspect of the viscoelastic model. We describe liquid 3He as a viscoelastic medium and aerogel as an elastic body. Since impurity scattering does not conserve the 3He-quasiparticle momentum, it causes friction between liquid and aerogel. The motions of the two systems are coupled with each other through the friction. We give the dispersion relations of both longitudinal and transverse sounds by solving the coupled equations of motion.
Co-existing Bose and Fermi Superfluid Mixtures in Aerogel
J.M. Parpia, G. Lawes, E. Nazaretski
Department of Physics and LASSP, Cornell University, Ithaca NY 14853, USA .
We have observed superfluidity in both the 4He rich and 3He rich components of helium mixtures confined in porous silica aerogel. By investigating mixtures with 4He fractions ranging from 3% to 90% we have established the occurrence of simultaneous Bose and Fermi superfluidity in this strongly inhomogeneous system. A positive frequency shift in the 4He superfluid slow mode as the sample is cooled below the 3He superfluid transition temperature indicates a strong coupling between the two superfluid components. The 3He Tc is quite insensitive to the 4He fraction in the mixture, suggesting that Tc is determined mainly by the 3He rich phase in the largest voids.