Spin-mass vortices have been observed to form in rotating superfluid 3He-B
following the absorption of a thermal neutron and a rapid transition from the
normal to superfluid state. The spin-mass vortex is a composite defect which
consists of a planar soliton (wall) which terminates on a linear core (string).
This observation fits well within the framework of a cosmological scenario for
defect formation, known as the Kibble-Zurek mechanism. It suggests that in the
early Universe analogous cosmological defects might have formed.Comment: RevTeX file, 5 pages, 2 figures, submitted to Phys. Rev. Lett.,
modified according to referee repor
