Pairing-bag excitations in small-coherence-length superconductors

Abstract

Localized baglike solutions in the pairing theory of superconductivity are studied. Starting from the Bogoliubov–de Gennes equations on a two-dimensional square lattice for half-filled negative-U Hubbard model, cigar- and star-shaped bags are numerically obtained, inside of which the order parameter is reduced, self-consistently trapping an added quasiparticle. These nonlinear excitations are important when the coherence length is small as for the new high-temperature superconductors. Several experimental consequences are discussed.