  X-band microwave spectroscopy is applied to study the cyclotron resonance in
Bi2Te3 exposed to ambient conditions. With its help, intraband transitions
between Landau levels of relativistic fermions are observed. The Fermi velocity
equals to 3260 m/s, which is much lower than has been reported in the
literature for samples cleaved in vacuum. Simultaneous observation of bulk
Shubnikov - de Haas oscillations by contactless microwave spectroscopy allows
determination of the Fermi level position. Occupation of topological surface
states depends not only on bulk Fermi level but also on the surface band
bending.
