Evidence for three-dimensional Dirac conical bands in TlBiSSe by optical and magneto-optical spectroscopy

TlBiSSe is a 3D Dirac semimetal that exists at the interface between a topological insulator, TlBiS${}₂$, and a trivial insulator, TlBiSe${}₂$. It is one of the few systems with an ideal band structure, exhibiting only conical dispersive bands over almost half an electronvolt. Here, the authors find a rare unequivocal signature of a 3D Dirac cone in its optical and magneto-optical properties, achieved by carefully controlled synthesis that places the Fermi level very close to the Dirac point.