The lattice site and delocalization of implanted μ+ particles were investigated in highly perfect single crystals at 0.02 to 88K. Below about 32K, the static binding of μ+ at the T1 interstitial sites (¼¼¼) was unambiguously confirmed. The data for different field strengths permitted the determination of the inherent and μ+-induced electric field gradients at the relaxed nuclear positions. The lattice expansion about the μ+ was found to be about 7%. Delocalization was observed at 32 to 52K. Low values of both the attempt frequency, 5 x 109/s, and the activation energy, Ea = 32.5meV, for hopping indicated under-barrier tunnelling diffusion in this temperature range. At 52 to 84K, the μ+ was again localized, the new μ+ site was characterized by a very low Gaussian relaxation rate, of about 0.08μ/s, for muon polarization.

Muon Dynamics at Low Temperatures in Indium. G.Solt, V.S.Egorov, C.Baines, D.Herlach, U.Zimmermann: Physica B, 2004, 348[1-4], 280-4