Time reversal symmetry-breaking states in two-band superconductors with interband pairing

If interband pairing is present in a two-band superconductor alongside the usual intraband pairing, then a variety of time reversal symmetry-breaking superconducting states become stable at lower temperatures. In these states, gap nodes can leave the Fermi surfaces and merge when the interband pairing is tuned. Also, the boundary modes change qualitatively upon increasing the interband pairing: flat zero-energy Andreev bound states gap out and transition to helical edge states.