Motion of Mu(+) in Transparent Conducting Oxides

Abstract

We have been investigating diamagnetic muonium centers in several optically transparent conducting oxides by zero field (ZF) muon spin depolarization. In this report we present our findings on single crystal beta - Ga2O3. ZF data from Ga2O3 are represented with a single static Kubo Toyabe (sKT) function over the whole scanned temperature range. Below room temperature we confirm shallow donor ionization. Between 400 and 500 K, sKT relaxation rates indicate local motion for Mu(+) among a set of similar sites. Above 500 K the relaxation rate decreases and reaches a plateau staying roughly constant up to 650 K. This behaviour is consistent with Mu(+) finding an energetically more favorable site with a smaller local dipolar field. Above 650K the depolarization rate starts to decrease again. We attribute this behavior to the onset of global Mu(+) diffusion. We have performed transverse field muon spin rotation experiments at low temperatures to investigate Mu(0) ionization. We will discuss the general trend of Mu(+) behavior and possibility of a second shallow Mu donor.