  The spatial modulation of the Fermi velocity for gapless Dirac electrons in
quantum materials is mathematically equivalent to the problem of massless
fermions on a certain class of curved spacetime manifolds. We study null
geodesic lensing through these manifolds, which are dominated by curvature
singularities, such as nematic singularity walls (where the Dirac cone flattens
along one direction). Null geodesics lens across these walls, but do so by
perfectly collimating to a local transit angle. Nevertheless, nematic walls can
trap null geodesics into stable or metastable orbits characterized by repeated
transits. We speculate about the role of induced one-dimensionality for such
bound orbits in 2D dirty d-wave superconductivity.
