  We study the effects of interband pairing in two-band s-wave and d-wave
superconductors with D4h symmetry in both time-reversal invariant as well as
time-reversal symmetry breaking states. The presence of interband pairing
qualitatively changes the nodal structure of the superconductor: nodes can
(dis)appear, merge, and leave high-symmetry locations when interband pairing is
tuned. Furthermore, in the d-wave case, we find that also the boundary modes
change qualitatively when interband pairing increases: flat zero-energy Andreev
bound states gap out and transition to helical edge states.
