Anelastic spectroscopy study of very diluted Zr–D tunnel systems in Nb single crystals

Abstract

The anelastic spectrum of the Nb 1− x Zr x D y alloy has been studied in the high dilution limit, down to x=1300 ppm and y=150 ppm. It was thus possible to single out the peaks associated with the most symmetric four-level systems (FLS). A narrow peak at 6 K (40 kHz) has been identified with the transitions between the intermediate levels of the FLS. The fact that such transitions are much slower than those between levels 1 and 4 and are not caused by the scattering with the conduction electrons is explained in terms of a vanishing matrix element for first order transitions involving the intermediate states of a centrosymmetric FLS.