Charge transport in Al2O3

Muon spin relaxation measurements in transverse and zero magnetic fields reveal muonium atom formation to be a thermally activated process in Al2O3 (sapphire) crystal. Experiments in electric fields up to 100 kV/cm unambiguously show that muonium is formed via the delayed channel of the radiolysis electron (created in the muon’s track) transport to the μ+. The formation of the “electronic polaron” is believed to be the limiting mechanism for electron transport in sapphire.