Muonium in diamond

Two muonium states have been found in diamond. "Normal" muonium shows an isotropic hyperfine interaction with a coupling constant $\frac{A}{h}=3711\mathrm{}\pm 21$ MHz. "Anomalous" muonium is described by a $〈111〉$ axially symmetric spin Hamiltonian with coupling constants extrapolated to 0 K $\frac{\left|A_{\parallel }\right|}{h}=167.98\mathrm{}\pm 0.06$ MHz and $\frac{\left|A_{\perp }\right|}{h}=392.59\mathrm{}\pm 0.06$ MHz. $A_{\parallel }$ and $A_{\perp }$ are of opposite sign, and they exhibit a temperature dependence describable by a Debye model. The amplitudes of the three anomalous muonium hyperfine transitions is zero applied field increase with increasing temperature and show relative variations which give information about muonium formation and indicate that anomalous muonium is the most stable state for muons in diamond. These diamond results are compared with those from the isostructural materials silicon and germanium.