Phase solitons and subgap excitations in two-band superconductors

A phase soliton is a topological defect peculiar to two-band superconductors, which is associated with a $2\pi$ winding of the relative phase of the two superconducting condensates. We study the quasiparticle spectrum in the presence of a single planar phase soliton. We show that the order parameter phase variation in each of the bands leads to the existence of subgap states bound to the soliton. Calculation of the soliton energy valid at all temperatures is presented, with the exact analytical results obtained for a simple soliton model.