  In an ideal bulk topological-insulator (TI) conducting surface states
protected by time reversal symmetry enfold an insulating crystal. However, the
archetypical TI, Bi2Se3, is actually never insulating; it is in fact a
relatively good metal. Nevertheless, it is the most studied system among all
the TIs, mainly due to its simple band-structure and large spin-orbit gap.
Recently it was shown that copper intercalated Bi2Se3 becomes superconducting
and it was suggested as a realization of a topological superconductor (TSC).
Here we use a combination of techniques that are sensitive to the shape of the
Fermi surface (FS): the Shubnikov-de Haas (SdH) effect and angle resolved
photoemission spectroscopy (ARPES) to study the evolution of the FS shape with
carrier concentration, n. We find that as n increases, the FS becomes 2D-like.
These results are of crucial importance for understanding the superconducting
properties of CuxBi2Se3.
