The effect of disorder on the relaxational properties of a quantum spin glass

We have studied the dynamic susceptibility in a quantum spin glass which is described by an Ising model in a transverse field, the latter introducing 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 ω, its amplitude is reduced and peaks are broadened, as quantum effects strengthen. Our results are in qualitative agreement with the experimentally studied crystal-field-split system of LiHoxY1−xF4 by Wu et al.