  We suggest a novel mechanism by which vorticity structuring and Taylor-like
velocity rolls can form in complex fluids, triggered by the linear instability
of one dimensional gradient shear banded flow. We support this with a numerical
study of the diffusive Johnson-Segalman model. In the steady vorticity
structured state, the thickness of the interface between the bands remains
finite in the limit of zero stress diffusivity, presenting a possible challenge
to the accepted theory of shear banding.
