Electrons in graphene—a two-dimensional (2D) form of carbon—behave a lot like massless particles. The phenomenon is at the heart of why graphene’s electrons have such a high mobility. According to theoretical calculations, similar behavior, and new effects, might be observed in 2D materials with crystal structures that share little likeness to graphene’s honeycomb lattice.

Graphene’s unusual electronic properties stem from its crystal structure, which gives rise to cone-shaped electronic energy bands that touch at points. Electrons that fill the bands near these points can be characterized by the same Dirac equation that describes photons and other relativistic particles traveling in 2D. This description isn’t perfect, however, because the bands near such “Dirac points” are distorted by the spin-orbit effect, an interaction between the spin and momentum of graphene’s electrons.

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