QUANTUM DIFFUSION OF LIGHT PARTICLES IN THE VORTEX STATE OF TYPE-II SUPERCONDUCTORS

The paper investigates the modification of the quasiparticle excitatio n spectrum of type-II superconductors caused by the formation of a flu x-line lattice and its effects on the tunnelling rate of light positiv ely charged interstitial particles. It is shown that near the upper cr itical field B-c2 the BCS-Gorkov equations predict for the spectral de nsity J(omega) (giving the probability of an energy exchange <(h)over bar omega> between particle and the electron system) ''superohmic'' be haviour proportional to omega(3/2) at low frequencies with a prefactor that depends on the position of the tunnelling centre relative to the flux-line lattice and on the angle between jump vector and the flux-l ines. As in normal-conducting metals, at higher frequencies J(omega) = 2K(e1)omega, is predicted. At low temperatures T the superohmic J(ome ga) leads to hopping rates nu proportional to T-2. At higher temperatu res a crossover to the Kondo law (nu proportional to T2Ke1-1) is expec ted.