  Two recent experiments successfully observed Landau levels in the tunneling
spectra of the topological insulator Bi2Se3. To mimic the influence of a
scanning tunneling microscope tip on the Landau levels we solve the
two-dimensional Dirac equation in the presence of a localized electrostatic
potential. We find that the STM tip not only shifts the Landau levels, but also
suppresses for a realistic choice of parameters the negative branch of Landau
levels.
