When the Fermi level is near the top of a band the carriers (holes) are
maximally dressed by electron-ion and electron-electron interactions. The
theory of hole superconductivity predicts that only in that case can
superconductivity occur, and that it is driven by undressing of the carriers
at the Fermi energy upon pairing. Indeed, experiments show that dressed hole
carriers in the normal state become undressed electron carriers in the
superconducting state. This leads to a description of superconductors as giant
atoms, where undressed time-reversed electrons are paired and propagate freely
in a uniform positive background. The pairing gap provides rigidity to the
wavefunction, and electrons in the giant atom respond to magnetic fields the
same way as electrons in diamagnetic atoms. We predict that there is an
electric field in the interior of superconductors and that the charge
distribution is inhomogeneous, with higher concentration of negative charge
near the surface; that the ground state of superconductors has broken parity
and possesses macroscopic spin currents, and that negative charge spills out
when a body becomes superconducting.Comment: Presented at the meeting 'Highlights in Condensed Matter Physics' in
honor of the 60th birthday of Prof. Ferdinando Mancini, May 9-11, 2003,
Salerno, Ital
