Collective Modes in nonuniform condensates
The most important feature of Superconductivity and Superfluidity is the presence of a condensate of correlated particles, described by the order parameter. One can excite waves of the order parameter where the entire condensate moves as a whole, and depending on complexity and symmetry of the condensate one can propagate different modes. We investigate what kind of new collective modes are present when one modifies the symmetry of the superconducting state.
We found that in the presence of a domain wall in the order parameter new superconductivity waves appear in the nonuniform region. Spectrum of these new modes can be gapless as a result of spontaneously broken translational symmetry.
Bound collective modes in nonuniform superconductors. A. R. Hammer, A. B. Vorontsov Phys. Rev. B 93, 014503 (2016)