Electric-field-induced muonium formation in sapphire

An applied electric field E is known to affect the probability f(Mu) of muonium formation in sapphire (Al2O3). The (small) amplitude of the long-lived diamagnetic mu(+)SR signal is increased slightly by positive E (in the direction of the muon's initial momentum), implying a reduction off,, as expected for delayed muonium formation where electrons originate "behind" the muon. In contrast to this, the initial amplitude of the short-lived diamagnetic signal (visible directly only at low T) is dramatically decreased (implying enhanced muonium formation at very early times) by positive E. This effect is not yet understood. (C) 2000 Elsevier Science B.V. All rights reserved.