Muonium Formation via Electron Transport in Silicon

Abstract

We report muon spin rotation measurements in $n$-type silicon from 10 to 310 K in electric fields up to 5 kV/cm. These experiments reveal the nature of the partition of neutral muonium centers into normal muonium $({\mathrm{Mu}}_{T}^{0})$ and anomalous muonium $({\mathrm{Mu}}_{\mathrm{BC}}^{0})$: Formation of ${\mathrm{Mu}}_{T}^{0}$ is consistent with epithermal processes prior to thermalization, while ${\mathrm{Mu}}_{\mathrm{BC}}^{0}$ is formed via electron transport to a thermalized positive muon. The spatial distribution of the excess electrons created in the ${\ensuremath{\mu}}^{+}$ ionization track is shown to be anisotropic with respect to the muon.