  Recent experiments show that shear-banded flows of semi-dilute worm-like
micelles in Taylor-Couette geometry exhibit a flow instability in the form of
Taylor-like vortices. Here we perform the non-axisymmetric linear stability
analysis of the diffusive Johnson-Segalman model of shear banding and show that
the nature of this instability depends on the applied shear rate. For the
experimentally relevant parameters, we find that at the beginning of the stress
plateau the instability is driven by the interface between the bands, while
most of the stress plateau is occupied by the bulk instability of the
high-shear-rate band. Our work significantly alters the recently proposed
stability diagram of shear-banded flows based on axisymmetric analysis.
