NMR relaxation in the localized regime in InSb

Abstract

Further experiments in doped InSb are reported on the anomalous NMR relaxation peak, the B-peak, first reported by Bridges and Clark. Data on the peak now extends up to donor concentrations of 8 × 10 21 m −3 and permits a sharp reduction in the number of possible explanations of the peak which remain plausible. The peak occurs well above the critical field required for magnetic freeze-out, and appears to follow a dependence of magnetic field at the peak, B B , against density, n D , of B B ∝ n 0.60±0.01 D at constant temperature. The possibility that the peak is due to the tuning of the ESR frequency through the typical electron hopping frequency ω H in the crystal is explored; a consequence of this model is that ω H must be dominated by nearest-neighbour hops, involving only a very small minority of the donor centres.