  Here we report on Landau level spectroscopy of an epitaxially grown thin film
of the topological insulator Sb2Te3, complemented by ellipsometry and
magneto-transport measurements. The observed response suggests that Sb2Te3 is a
direct-gap semiconductor with the fundamental band gap located at the \Gamma
point, or along the trigonal axis, and its width reaches Eg = 190 meV at low
temperatures. Our data also indicate the presence of other low-energy extrema
with a higher multiplicity in both the conduction and valence bands. The
conclusions based on our experimental data are confronted with and to a great
extent corroborated by the electronic band structure calculated using the GW
method.
