Theories for Superfluid 3 He
Erkki Thuneberg
Department of Physical Sciences, University of Oulu, Finland
Superfluid 3 He is an attractive system for theoretical studies because of the interplay of several theories
that work on different length scales. In particular the quasiclassical theory, which works on the scale of
the superfluid coherence length ξ0 ∼ 10 nm, forms a firm foundation for the Ginzburg-Landau theory
and for different hydrodynamic theories, which work on larger scales in the A and B superfluid phases.
As examples I will discuss three topics. (i) The Josephson effect has been experimentally studied in
3
He flowing through narrow holes. The current-phase relation and other properties are different from
superconducting weak links. This can be explained by the coupling of mass current with spin degrees of
freedom. In the presence of a pressure bias, part of the dc current arises from multiple-Andreev-reflection
process and part from oscillation of the spin-orbit texture and radiation of spin waves. (ii) Superfluid
3
He is especially known for its rich vortex structures. I discuss a few exotic objects, the vortex sheet
in particular. A striking confirmation of the theory is the agreement with measured NMR frequency
shifts. (iii) Liquid 3 He is a naturally pure substance. For many purposes this is an advantage, but it is
also interesting to study the effect of impurities on this unconventional superfluid. Several experiments
have studied 3 He in aerogel, which is an open network mimicking impurity. I discuss the models used to
describe this system.
Sorting category: Aa Quantum gases, fluids and solids
Keywords: superfluid 3 He, quasiclassical theory, Josephson effect, vortices, aerogel
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