Role of the transition state in muon implantation

Abstract

In muon-spin-rotation experiments, positive muons are implanted in the material and come to rest in the unrelaxed host lattice. The formation of the final configuration requires a lattice relaxation which does not occur instantly. The present paper is concerned with the transition from the initial stopping state to the final muon configuration. We identify the often observed fast relaxing signal in muon experiments (e.g., in several oxides studied recently) with the transition state in this conversion process. This state is paramagnetic with a small hyperfine interaction (in the order of MHz) which fluctuates and averages to almost zero. Because of its apparent diamagnetic frequency behavior, the fast signal was in the past assigned to Mu + or Mu − . We present evidence that this state is actually paramagnetic. The model presented in this paper is of importance for the interpretation of past and future μSR measurements.

Barrier model in muon implantation and application to Lu2O3

“…The other part stems from neutral muonium which was formed in the charge exchange process but has converted to a diamagneticlike configuration. We distinguish two possibilities; either the electron remains near the muon but is in a transition state [17] with a weak hyperfine interaction which fluctuates and averages to almost zero, or the electron is lost during the reaction of muonium with the lattice and the μ + state is observed. Experimentally, we cannot distinguish between these two possibilities in the present case.…”

“…The usual interpretation in the past was that it relates to delayed capture or loss of an electron by the muon center. We showed in a recent paper [17] that in the case of zirconia the delay is caused by the lattice rearrangement necessary to accommodate muonium. We proposed the following process [17]: Muons which have picked up an electron during the slowing down process come to rest at an interstitial site as compact atomic muonium with a large hyperfine interaction.…”

“…We showed in a recent paper [17] that in the case of zirconia the delay is caused by the lattice rearrangement necessary to accommodate muonium. We proposed the following process [17]: Muons which have picked up an electron during the slowing down process come to rest at an interstitial site as compact atomic muonium with a large hyperfine interaction. However, this electronic configuration is not stable and the electron spreads out forming a shallow donorlike state with a weak and fluctuating hyperfine interaction.…”

CdS versus ZnSnO buffer layers for a CIGS solar cell: a depth-resolved analysis using the muon probe

“…The diamagnetic fraction was found to be smaller than unity for most of the measurements. This indicates that the muons experience a strong interaction during their implantation stage, reducing the formation probability of the final bound configuration [4,[8][9][10][11][12][13].…”

Modelling isolated hydrogen impurity in Lu2O3 with muonium spectroscopy

“…3). However, we recently found [16], that there is also the possibility that a fairly long-lived (ns to µs) transition state is formed from which the final configurations arise (blue and red arrow). The transitions are hindered by barriers (energy values on the arrows in the Fig.…”