Topological phonons and Weyl lines in 3 dimensions
  Topological mechanics and phononics have recently emerged as an exciting field of study. Here we introduce and study generalizations of the three-dimensional pyrochlore lattice that have topologically protected edge states and Weyl lines in their bulk phonon spectra, which lead to zero surface modes that flip from one edge to the opposite as a function of surface wavenumber. 
Olaf Stenull, C. L. Kane and T. C. Lubensky
cond-mat.soft