Inhomogeneous States of Nonequilibrium Superconductors: Quasiparticle Bags and Antiphase Domain Walls

TL;DR

This paper investigates the complex inhomogeneous states in nonequilibrium superconductors, revealing that quasiparticles tend to form topological textures like antiphase domain walls, which can be experimentally detected.

Contribution

It introduces the concept of quasiparticle segregation into antiphase domain walls as the lowest-energy configuration in inhomogeneous superconductors.

Findings

Antiphase domain walls are detectable via optical absorption and NMR.

Quasiparticles rarely form self-trapped bag states at zero temperature.

Extrinsic defects can stabilize quasiparticles at low concentrations.

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 where quasiparticles segregate into antiphase domain walls between superconducting regions whose order-parameter phases differ by $\pi$. 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.