Neutron reflectometry was used to investigate the deuterium uptake in a thin metal superlattice that displays
an anisotropic elastic response Fe0.5V0.5 /V 
6/21 monolayers. We see evidence of the presence of a coexistence
region which has never before been seen in vanadium-based superlattices. The loading process is
completely reversible from which we conclude that the phases must be coherent, in stark contrast to bulk VDx,
where the two-phase region displays hysteresis. The deuterium-induced volume expansion exhibits changes in
slope that correlate with the plateau region and the expansion is comparable and even larger than in the bulk.
The spectacular cooperation between the elastic fields seems to be found only in one-dimensionally confined
structures with biaxial compressive strain states.