FIELD-DEPENDENCE OF THE LONGITUDINAL MUON POLARIZATION FOR ANOMALOUS MUONIUM

An unusual longitudinal-magnetic-field dependence of the muon polariza tion for anomalous muonium (Mu) in polycrystalline semiconductor targ ets is predicted, and has been observed for Si. As a function of field , the experimentally measured muon polarization at 53 K exhibits a cus p, i.e., a discontinuous jump in the slope from negative to positive, at 340(5) mT, in good agreement with theory. This occurs because the e ffective field on the mu(+) vanishes at this external field as the ang le between it and the Mu symmetry axis approaches 90 degrees. At 200 K no cusp is seen because Mu has been thermally annihilated. Fraction al populations of the different muonium species are derived from the 5 3-K data. All Mu and other anisotropic centers, including molecular r adicals, should exhibit such a cusp, allowing the possibility of obser ving such species even in disordered or amorphous solids where spectro scopic detection might be impossible. Integral counting (and therefore very high data rates) can be used for these observations.