  Using low temperature scanning tunneling spectroscopy, we probe the Landau
levels of the topologically protected state of Sb2Te3(0001) after in-situ
cleavage of a single crystal. Landau levels are visible for magnetic fields B >
2 T at energies, which confirm the Dirac type dispersion including the zeroth
Landau level. We find different Dirac velocities for the lower and the upper
part of the Dirac cone in reasonable agreement with previous density functional
theory data. The Dirac point deduced from the zeroth Landau level shifts by
about 40 meV between different areas of the sample indicating long range
potential fluctuations. The local potentials are correlated to different local
defect densities varying slightly stronger than expected from a statistical
distribution. The quasiparticle lifetime deduced from the width of the Landau
level peaks decreases close to inversely with the electron energy with respect
to the Fermi level. Consequently, we attribute the peak width to a dominating
scattering of the hot quasiparticles by electron-electron interaction.
