Inhomogeneous states of nonequilibrium superconductors: Quasiparticle bags and antiphase domain walls

Abstract

Nonequilibrium properties of short-coherence-length $s$-wave superconductors are analyzed in the presence of extrinsic and intrinsic inhomogeneities. In general, the lowest-energy configurations of quasiparticle excitations are topological textures into which quasiparticles segregate and that are described as antiphase domain walls between superconducting regions whose order parameter phases differ by $\ensuremath{\pi}$. Antiphase domain walls can be probed by various experimental techniques, for example, by optical absorption and NMR. At zero temperature, quasiparticles seldom appear as self-trapped bag states. However, for low concentrations of quasiparticles, they may be stabilized in superconductors by extrinsic defects.