THE EFFECT OF DISORDER ON THE RELAXATIONAL PROPERTIES OF A QUANTUM SPIN-GLASS

We have studied the dynamic susceptibility in a quantum spin glass whi ch is described by an Ising model in a transverse field, the latter in troducing quantum effects in an otherwise classical problem, using the mean field theory. It is shown that the frequency of the peak of the susceptibility shifts towards higher values of omega, its amplitude is reduced and peaks are broadened, as quantum effects strengthen. Our r esults are in qualitative agreement with the experimentally studied cr ystal-field-split system of LiHoxY1-xF4 by Wu et al.