47 research outputs found
Distinguishing Ion Dynamics from Muon diffusion in Muon Spin Relaxation
We propose a model to describe the fluctuations in the internal magnetic
field due to ion dynamics observed in the muon spin relaxation (SR) by an
Edwards-Anderson type autocorrelation function that separates the quasi-static
and dynamic components of the correlation by a parameter (where ). Our Monte Carlo simulations for this model showed that the time
evolution of muon spin polarization deviates significantly from the Kubo-Toyabe
(KT) function. To further validate the model, the results of simulations were
compared with the SR spectra observed in a hybrid organic-inorganic
perovskite FAPbI [with FA referring to HC(NH], where local field
fluctuations associated with the rotational motion of FA molecules and
quasi-static fields from the PbI lattice are presumed to coexist. The
least-squares curve fitting showed reasonable agreement with the model with
, and the fluctuation frequency of the dynamical component was
obtained. This result opens the door to the possibility of experimentally
distinguishing fluctuations due to dynamics of ions around muons from those due
to self-diffusion of muons. Meanwhile, it suggests the need to carefully
consider the spin relaxation function when applying SR to the issue of ion
dynamics.Comment: 7 pages, 4 figures, Supplemental Material available at the JPSJ sit
Electronic structure of the muonium center as a shallow donor in ZnO
The electronic structure and the location of muonium centers (Mu) in
single-crystalline ZnO were determined for the first time. Two species of Mu
centers with extremely small hyperfine parameters have been observed below 40
K. Both Mu centers have an axial-symmetric hyperfine structure along with a
[0001] axis, indicating that they are located at the AB_{O,//} and BC_{//}
sites. It is inferred from their small ionization energy (~6 meV and 50 meV)
and hyperfine parameters (~10^{-4} times the vacuum value) that these centers
behave as shallow donors, strongly suggesting that hydrogen is one of the
primary origins of n type conductivity in as-grown ZnO.Comment: 4 pages, 4 figures, submitted to PR