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We report electron paramagnetic resonance (EPR) experiments of phosphorus donors in isotopically controlled silicon single crystals. By varying the concentration of the ^29Si isotope, f, from 0. 075% to 99. 2%, we systematically study the effect of the environmental nuclear spins on the donor-electron spin. We find excellent agreement between experiment and theory for decoherence times due to nuclear-induced spectral diffusion, clarifying that the nuclear-induced decoherence is dominant in the range of f studied. We also observe that the EPR linewidth shows a transition from the square-root dependence to the linear dependence on f, in agreement with theoretical predictions.
Abe et al. (Thu,) studied this question.