  We theoretically investigate 3D layered crystals of alternating graphene and
hBN layers with different symmetries. Depending on the hopping parameters
between the graphene layers, we find that these synthetic 3D materials can
feature semimetallic, gapped, or Weyl semimetal phases. Our results demonstrate
that 3D crystals stacked from individual 2D materials represent a synthetic
materials class with emergent properties different from their constituents.
