Dirac semimetals are critical states of topologically distinct phases. Such gapless topological states have been accomplished by a band-inversion mechanism, in which the Dirac points can be annihilated pairwise by perturbations without changing the symmetry of the system. Here, scientists in China report an experimental observation of Dirac points that are enforced completely by the crystal symmetry using a nonsymmorphic phononic crystal. Novel topological surface states are demonstrated in their experiments.
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Source: Phys.org