  We develop a theory of the rectification effect in a double-layer system
where both layers are superconductors, or one of the layers is a normal metal.
The Coulomb interaction is assumed to provide the dominant coupling between the
layers. We find that superconducting fluctuations strongly enhance the drag
conductivity, with rectification most pronounced when both layers are
superconductors. In view of their distinct dependence on temperature near Tc
and layer separation, drag measurements based on a Giaever transformer could
distinguish whether rectification occurs due to fluctuating pairs or
inductively coupled fluctuating vortices.
