High-field spin dynamics of a spin-1/2 Heisenberg chain

The field dependence of the nuclear spin relaxation rate (T-11) is studied in a linear spin-1/2 Heisenberg antiferromagnetic chain above the critical field. Various mechanisms playing dominant roles for T1-1 in different field regimes are discussed. The effect of magnon diffusion is examined. We find that when the magnon collision rate (tau-1) is much larger than the nuclear Zeeman frequency (ω), T1-1 is enhanced by a factor (ωtau)sup(-1/3) at high temperatures and its field dependence changes drastically. (orig.)