Flat band in the core of topological defects: bulk-vortex correspondence in topological superfluids with Fermi points
G. E. Volovik
Low Temperature Laboratory, Aalto University, School of Science and Technology, FI-00076 AALTO, Finland
Landau Institute for Theoretical Physics RAS, 119334 Moscow, Russia
Abstract
We discuss the dispersionless spectrum with zero energy in the linear
topological defects - vortices. The flat band emerges inside the vortex living in the bulk
medium containing topologically stable Fermi points in momentum space. The boundaries
of the flat band in the vortex are determined by projections of the Fermi points in bulk to
the vortex axis. This bulk-vortex correspondence for flat band is similar to the bulk-surface
correspondence discussed earlier in the media with topologically protected lines of zeroes.
In the latter case the flat band emerges on the surface of the system, and its boundary is
determined by projection of the bulk nodal line on the surface.