  We propose a realizable device design for an all-electrical robust valley
filter that utilizes spin protected topological interface states hosted on
monolayer 2D-Xene materials with large intrinsic spin-orbit coupling. In
contrast with conventional quantum spin-Hall edge states localized around the
$X$-points, the interface states appearing at the domain wall between
topologically distinct phases are either from the $K$ or $K^{'}$ points, making
them suitable prospects for serving as valley-polarized channels. We show that
the presence of a large band-gap quantum spin Hall effect enables the spatial
separation of the spin-valley locked helical interface states with the valley
states being protected by spin conservation, leading to a robustness against
short-range non-magnetic disorder. By adopting the scattering matrix formalism
on a suitably designed device structure, valley-resolved transport in the
presence of non-magnetic short-range disorder for different 2D-Xene materials
is also analyzed in detail. Our numerical simulations confirm the role of
spin-orbit coupling in achieving an improved valley filter performance with a
perfect quantum of conductance attributed to the topologically protected
interface states. Our analysis further elaborates clearly the right choice of
material, device geometry and other factors that need to be considered while
designing an optimized valleytronic filter device.
