Half quantum vortices. Landau Days 2014. Mineev V.P..

24 June, Landau Days 2014, Mineed V.P..
"The superfluid He-3 under rotation has been discussed first
in 1977 by G.E.Volovik and N.B.Kopnin.
Since that time the singular single quanta vortices as
well nonsingular vortices with 2 quanta of circulation have
been revealed in rotating He-3A. He-3A supports also
the existence of vortices with half-quantum of circulation.
However, the half-quantum vortices in open geometry always
possess an extra energy due to spin-orbital coupling leading
to formation of domain wall at distances larger than dipole
length ~10 -3 cm from vortex axis. Fortunately the same
magnetic dipole-dipole interaction does not prevent
the existence of half-quantum vortices in the polar phase
of superfluid He-3 recently discovered in peculiar porous media
"nematically ordered" aerogel."