Determination of the electronic structure of anomalous muonium in GaAs from nuclear hyperfine interactions

Nuclear hyperfine structure of the anomalous muonium center (Mu*) in GaAs has been resolved in muon-spin-rotation frequency spectra and studied in detail by level-crossing-resonance spectroscopy. A comparison of the measured hyperfine parameters with the free-atom values indicates that 38% (45%) of the spin density is on one Ga (As) on the 〈111〉 symmetry axis of Mu* with the ratio of p to s spin density equal to about 4 (23). These results support a recently proposed model in which Mu* is a neutral interstitial located close to the center of a Ga---As bond.