Weyl points of mechanical diamond

Yuta Takahashi, Toshikaze Kariyado, Yasuhiro Hatsugai

Published 2018-01-21Version 1

A spring-mass model arranged in a diamond structure---mechanical diamond---is analyzed in terms of topology in detail. We find that, additional springs connecting the next-nearest-neighboring pairs of mass points and the modulation of the mass parameters to the pristine mechanical diamond generates several pairs of Weyl points in the frequency dispersion. Evolution of the Weyl point mapping in the Brillouin zone against uniform outward tension is shown and explained from the view point of the point group symmetry, especially tetrahedral symmetry of the NNN springs. Interestingly, there happens a rapid transmutation of the monopole charges of the Weyl points as the tension changes. We also show Fermi arcs as surface modes in the case that anisotropy is introduced in the model.