  Shubnikov de Haas (SdH) oscillations and Angle Resolved PhotoEmission
Spectroscopy (ARPES) are used to probe the Fermi surface of single crystals of
Bi2Se3. We find that SdH and ARPES probes quantitatively agree on measurements
of the effective mass and bulk band dispersion. In high carrier density
samples, the two probes also agree in the exact position of the Fermi level EF,
but for lower carrier density samples discrepancies emerge in the position of
EF. In particular, SdH reveals a bulk three-dimensional Fermi surface for
samples with carrier densities as low as 10^17cm-3. We suggest a simple
mechanism to explain these differences and discuss consequences for existing
and future transport studies of topological insulators.
