Quantum transport of electronic polarons in sapphire

The formation of an electronic polaron is believed to be the limiting mechanism for electron transport in sapphire (Al₂O₃). Measurements of the spin depolarization of positive muons (μ⁺) implanted in a sapphire crystal in electric fields up to 100 kV/cm show that the muonium atom (Mu=μ⁺e^-) is formed via transport to the μ⁺ of a radiolysis electron created in the muon’s track. At high temperature, electron transport is consistent with a two-phonon mechanism of quantum diffusion, while at low temperature it is temperature independent due to a crossover to a one-phonon mechanism.