Nature Mater. (2014)

Much of the excitement surrounding graphene and the wider class of so-called Dirac materials arises from their unusual electronic structure, in which low-energy electrons effectively mimic the motion of relativistic high-energy particles known as Dirac fermions. A notable recent addition to this family has been that of three-dimensional Dirac semimetals, bulk 'analogues' of graphene that have been realized in materials such as Na3Bi and Cd3As2.

The wide variety of phenomena associated with graphene is well known, and it is natural to ask if the physics of three-dimensional Dirac semimetals is equally rich. In fact, Cd3As2 has been studied for decades because of its high carrier mobility, but without a clear understanding of its full band structure. Recent theoretical studies also predict several novel transport properties.

Tian Liang and colleagues now report an unexpected characteristic of Cd3As2. In addition to a giant magnetoresistance, they observed a suppression of the backscattering of electrons in zero magnetic field, which resulted in an exceptional mobility rivalling the record values measured in epitaxially-grown semiconductors. They attributed this to a topological protection mechanism inherent to the system's band structure, which suggests further surprises may be just around the corner.