Phonon-assisted spin diffusion in solids

The spin flip-flop transition rate is calculated for the case of spectral s pin diffusion within a system of dipolarly coupled spins in a solid where t he lattice vibrations are present, Long-wavelength acoustic phonons time-mo dulate the interspin distance r(ij) and enhance the transition rate via the change of the 1/r(ij)(3) term in the coupling dipolar Hamiltonian, The pho non-assisted spin diffusion rate is calculated by the golden rule in the De bye approximation of the phonon density of states. The coupling of the spin s to the phonons introduces temperature dependence into the transition rate , in contrast to the spin diffusion in a rigid lattice, where the rate is t emperature-independent. The direct (one-phonon absorption or emission) proc esses introduce a linear temperature dependence into the rate at temperatur es not too close to T = 0, Two-phonon processes introduce a more complicate d temperature dependence that again becomes simple analytical for temperatu res higher than the Debye temperature, where the rate is proportional to T- 2, and in the limit T --> 0, where the rate varies as T-7. Raman processes (one-phonon absorption and another phonon emission) dominate by far the pho non-assisted spin flip-flop transitions, (C) 2000 Academic Press.