  We study the Andreev and normal reflection processes -- retro as well as
specular -- in a bilayer graphene-superconductor junction where equal and
opposite displacement fields are applied for the top and bottom layers to
induce a band gap. By employing the Dirac-Bogoliubov-de Gennes equation for the
gapped bilayer graphene-superconductor junction, we calculate the reflections
probabilities within the scattering theory approach. The subgap conductance,
calculated in the framework of Blonder-Tinkham-Klapwijk formalism, shows the
contribution from the Andreev retro-reflection (specular-reflection) when the
applied bias voltage is below (above) the Fermi energy. Notably, both retro and
specular reflections are modified in the presence of the displacement field,
and the retro-to-specular crossover gets amplified when the displacement field
is relatively small. They can be further tuned to either specular or retro
Andreev reflection by adjusting the Fermi energy. Furthermore, our study
reveals the simultaneous existence of double Andreev reflections and double
normal reflections when the displacement field becomes comparable to the
interlayer coupling strength. The existence of the normal retro-reflection
process in a bilayer graphene-superconductor junction is a new finding which
shows a distinctive feature in the conductance that can be experimentally
verified.
