  We propose a tunable topological Josephson junction in silicene where
electrostatic gates could switch between a trivial and a topological junction.
These aspects are a consequence of a tunable phase transition of the
topologically confined valley-chiral states from a spin-degenerate to a
spin-helical regime. We calculate the Andreev bound states in such a junction
analytically using a low-energy approximation to the tight-binding model of
silicene in proximity to s-wave superconductors as well as numerically in the
short- and long-junction regime and in the presence of intervalley scattering.
Combining topologically trivial and non-trivial regions, we show how
intervalley scattering can be effectively switched on and off within the
Josephson junction. This constitutes a topological Josephson junction with an
electrically tunable quasiparticle poisoning source.
