Coherent Excited States in the Theory of Superconductivity: Gauge Invariance and the Meissner Effect
Abstract
We discuss the coherent states generated in the Bardeen, Cooper, and Schrieffer theory of superconductivity by the momentum displacement operator ρ_{Q}=nexp(iQ.r_{n}). Without taking into account plasma effects, these states are like bound Cooper pairs with momentum ℏQ and energies lying in the gap, and they play a central role in the explanation of the gauge invariance of the Meissner effect. Longrange Coulomb forces recombine them into plasmons with equations of motion unaffected by the gap. Central to the argument is the proof that the nongaugeinvariant terms in the Hamiltonian of Bardeen, Cooper, and Schrieffer have an effect on these states which vanishes in the weakcoupling limit.
 Publication:

Physical Review
 Pub Date:
 May 1958
 DOI:
 10.1103/PhysRev.110.827
 Bibcode:
 1958PhRv..110..827A