The local electronic structure of muons (Mu) as dilute pseudohydrogen in single-crystalline $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ has been studied by the muon spin rotation/relaxation $\left(\mu \mathrm{SR}\right)$. High-precision measurements over a long time range of $\sim 25\mu \mathrm{s}$ have clearly identified two distinct Mu states: a quasistatic Mu $\left({\mathrm{Mu}}_1\right)$ and fast-moving Mu $\left({\mathrm{Mu}}_2\right)$. By comparing this result with predictions from the recently established ambipolarity model, these two states are respectively attributed to the relaxed-excited states associated with the donor $\left(E^{+/0}\right)$ and acceptor $\left(E^{-/0}\right)$ levels predicted by density functional theory (DFT) calculations for the interstitial H. Furthermore, the local electronic structure of ${\mathrm{Mu}}_1$ is found to be an OMu-bonded state with three-coordinated oxygen. The structure is almost identical with the thermal equilibrium state of H, and it is found to function as an electron donor. The other ${\mathrm{Mu}}_2$ is considered to be in the hydride state $\left({\mathrm{Mu}}^{-}\right)$ from the ambipolarity model, suggesting that it is in fast diffusion motion through the short-lived neutral state due to the charge exchange reaction with conduction electrons $({\mathrm{Mu}}^{-}\rightleftarrows {\mathrm{Mu}}^0+e^{-})$.

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• Defects
• Diffusion
• Electronic structure
• Ionic transport
• Semiconductors
• Wide band gap systems
• Density functional theory
• Muon spin relaxation & rotation