Determination of the energy band gap of Bi 2 Se 3

Despite intensive investigations of Bi 2 Se 3 in past few years, the size and nature of the bulk energy band gap of this well-known 3D topological insulator still remain unclear. Here we report on a combined magneto-transport, photoluminescence and infrared transmission study of Bi 2 Se 3 , which unambiguously shows that the energy band gap of this material is direct and reaches E g = (220 ± 5) meV at low temperatures.