THE ROLE OF ONE-PHONON AND FEW-PHONON PROCESSES IN THE QUANTUM DIFFUSION OF LIGHT PARTICLES IN SUPERCONDUCTORS

The hopping motion of charged light particles in superconducting metal s is discussed within the framework of a two-state model. In addition to the coupling to the superconducting electrons, the influence of pho nons is investigated. It is shown that sufficiently far below the crit ical temperature the hopping rate is dominated by one-phonon processes if the static energy shifts between the particle ground states (so-ca lled energy asymmetries) are finite but smaller than twice the BCS ene rgy gap. The role of special two-phonon processes (named diphonon proc esses) resulting from non-linear coupling to the lattice is investigat ed. In the limit of energy asymmetries larger than twice the BCS energ y gap phonon coupling does not crucially influence the jump rates.