Nuclear spin decoherence of neutralP31donors in silicon: Effect of environmentalSi29nuclei

Spectral diffusion arising from $²⁹\mathrm{Si}$ nuclear spin flip-flops, known to be a primary source of electron spin decoherence in silicon, is also predicted to limit the coherence times of neutral donor nuclear spins in silicon. Here, the impact of this mechanism on $³¹\mathrm{P}$ nuclear spin coherence is measured as a function of $²⁹\mathrm{Si}$ concentration using $X$-band pulsed electron nuclear double resonance. The $³¹\mathrm{P}$ nuclear spin echo decays show that decoherence is controlled by $²⁹\mathrm{Si}$ flip-flops resulting in both fast (exponential) and slow (nonexponential) spectral diffusion processes. The decay times span a range from 100 ms in crystals containing 50% $²⁹\mathrm{Si}$ to 3 s in crystals containing 1% $²⁹\mathrm{Si}$. These nuclear spin echo decay times for neutral donors are orders of magnitude longer than those reported for ionized donors in natural silicon. The electron spin of the neutral donors ``protects'' the donor nuclear spins by suppressing $<sup>29</sup>\mathrm{Si}$ flip-flops within a ``frozen core,'' as a result of the detuning of the $²⁹\mathrm{Si}$ spins caused by their hyperfine coupling to the electron spin.