Electronic, Magneto-Optical, and Magnetotransport Properties of the Topological Insulator Sb 2 Te 2 Se

The structural, magneto-optical, and magnetotransport properties as well as the electronic band structure of the bulk crystalline topological insulator (TI) Sb2Te2Se, grown by the vertical Bridgman technique, were studied. The high structural quality of the grown crystals was established by x-ray diffraction and Raman spectroscopy. Angular resolved photoelectron spectroscopy revealed a single Dirac cone with the Dirac point, away from the valence as well as conduction bands, 0.22 eV above the Fermi level. The magnetotransport data exhibited a distinct single-frequency Shubnikov-de Haas oscillation in the magnetic fields above B = 10 T. The Lifshitz-Kosevich analysis of the data suggests that this oscillation originates from the Dirac-type states. A sharp fundamental absorption edge in the mid-infrared transmission spectra measured at 4.2 K demonstrated a direct band gap of 0.377 eV located at a momentum of 0.1 & Aring;-1 along the P- K directions of the Brillouin zone. A two-band model developed for massive Dirac electrons in the bulk of topological insulators with the direct band gap at a non-& Gcy; point suggests hyperbolic dispersion relations for the conduction and valence bands displaying the full electron-hole symmetry. Equal magnitude of the electron and hole effective masses me mh 0.21m0 and g factors ge gh 10 were estimated.