Slow phonon vortices and defect modes in periodic nano-waveguides
  We identify a broad class of phonon modes with persistent vortex fluxes at arbitrarily slow propagating velocities in periodic nano-waveguides. Such phonon vortices are associated with the split band-edges in dispersion dependencies, which can be engineered by waveguide design. Modulations introduced in such waveguides can support a pair of defect cavity phonon modes with an arbitrarily small frequency splitting. These features can find applications for sensing and nano-manipulation. 
Yue Sun, Anton S. Desyatnikov, and Andrey A. Sukhorukov
physics.optics cond-mat.mes-hall