Electron spin coherence and electron nuclear double resonance of Bi donors in natural Si

We have shown that the electron spin coherence times of Si:Bi donors in natural silicon are limited by the same mechanism of spectral diffusion as seen in Si:P, though the smaller Bohr radius of the Bi donor leads to $\sim30\%$ longer T$_2$ times (up to 0.8~ms). We have mapped out the 36 ENDOR transitions observable at X-band arising from the $I=9/2$ nuclear spin of $^{209}$Bi, going up to 1.3~GHz. We also demonstrate the transfer of electron spin coherence to and from the $^{209}$Bi nuclear spin with a fidelity of $\sim63\%$. Using pulsed ESR at W-band (100~GHz), we observe optically-induced dynamic nuclear polarisation, consistent with the mechanism of exciton capture proposed in by T. Sekiguchi \emph{et al.}. Finally, we explore the zero-field splitting of 7.5~GHz in this system, within the context of coupling to superconducting resonators.