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 (mu(+)) implanted in a sapphire crystal in electric fields up to 100 kV/cm show that the muonium atom (Mu=mu(+)e(-)) is formed via transport to the mu(+) 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.