The structural, magneto-optical, and magnetotransport properties as well as the electronic band structure of the bulk crystalline topological insulator (TI) ${\mathrm{Sb}}_2{\mathrm{Te}}_2\mathrm{Se}$, 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 ${\AA }^{-1}$ along the $\overline{\mathrm{\Gamma }}\text{−}\overline{K}$ 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-Г 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 $m_e\approx m_h\approx 0.21m_0$ and $g$ factors $g_e\approx g_h\approx 10$ were estimated.

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• Electronic structure
• Magneto-optics
• Magnetotransport
• Topological materials
• Angle-resolved photoemission spectroscopy