Speaker
Description
We study the μ+ dynamics in CaF2 in a wide temperature range between 10K and 290K using ZF and LF μ+SR experiments. The analysis of the muon spin polarization function A(t) at all temperatures in zero field (figure (a)) and longitudinal magnetic field is done by a quantum simulation of the static muon spin interacting with 2 nearest neighbor and 8 next-nearest neighbor flourine nuclear moments at relaxed sites calculated by DFT+μ on a 2x2x2 supercell. A considerable dynamical relaxation above 200 K caused by muon diffusion is accurately described by combining the static relaxation function with strong collision muon hopping. We find a thermally activated muon tunneling process between F-μ-F states with an activation energy Ea =0.24 eV.
We use the climbing image nudge elastic band (ciNEB) method to estimate the energy barrier between the two lowest muon stopping sites μ1 and μ2 (figure (b)). The activation energy was corrected by accounting for the zero-point energy (ZPE) of the muon at both the stable sites (μ1 or μ2) and the transition state (μTS) (see figure (c)) leading to Ea = 0.5 eV implying that thermally activated tunnelling processes are important.
[Figure 1:(a) temperature dependent ZF µSR spectra on Ca F2, (b) sequence of muon positions between two F-µ-F sites generated by nudged eleastic band and DFT+µ (c) total energy along nduged eleastic band pathway (blue), corrected by ZPE (red)]]fig1
| henning.klauss@tu-dresden.de | |
| Funding Agency | DFG |
