  We study the crossover in a zero temperature superconducting nanofilm from a
single to a double superconducting slab induced by a tunable insulating
potential barrier in the middle. The single phase superconducting ground state
of this heterostructure is shown to be intrinsically multigapped and to have a
new type of resonance caused by the strength of the barrier, thus distinct from
the Thompson-Blatt shape resonance which is caused by tuning the thickness of
the film. Single particle electronic states are strongly or weakly affected
according to their parity (even or odd) with respect to the insulating barrier.
The lift of the parity degeneracy at finite barrier strength reconfigures the
pairing interaction and leads to a multigapped superconducting state with
interaction driven resonances.
