  The topological properties of a multiband topological superconductor in two
dimensions are studied, when the latter is obtained by introducing electron
pairing in an otherwise topological insulator. The type of pairing, doping and
Fermi surface topology play an essential role. Considering the Andreev
reflection problem, we use a previously developed quantum waveguide theory for
multiorbital systems and find that, when the Fermi surface has several pockets,
this theory retrieves the correct number of Majorana fermion states as
predicted by the topological index. By varying band structure parameters, the
Fermi surface topology of the normal phase can be made to change, whereby the
number of Majorana modes also varies. We calculate the effect of such
transitions on the Andreev differential conductance.
