Muon localization along a six-fold ring-shaped site and muon quantum hopping in GdNi 5

Abstract

In GdNi 5, the muon localizes at the 3 f interstitial site and below ∼80 K a second muon site becomes populated, either at the 6 m or 6 k site. These latter sites are located in a ring surrounding the (0, 0, 1 2 ) site and the muon occupies all six sites within the time range of the experiment (10 −9 s). This ring site is metastable and the muon hops to the preferred 3 f site. We determine the mean time of stay of the muon in the ring site and show that it is governed by a multi-phonon quantum diffusion process. The coincidence energy is measured to be E a=272 (10) K and the tunneling matrix element J=0.11 (2) meV.