Dynamic nuclear polarization and ESR hole burning in As doped silicon

TL;DR

This study investigates how dynamic nuclear polarization affects silicon-29 nuclei in doped silicon at very low temperatures and high magnetic fields, revealing different effects of solid and Overhauser mechanisms on ESR line features.

Contribution

It provides experimental insights into the ESR line modifications and nuclear spin diffusion processes during DNP in silicon doped with arsenic, highlighting the effects of different DNP mechanisms.

Findings

Solid effect DNP creates ESR holes and peaks separated by super-hyperfine interaction.

Overhauser DNP produces a narrow ESR hole affecting remote nuclei.

Nuclear spin diffusion coefficient estimated at 8(3)×10⁻³ mG²/s.

Abstract

We present an experimental study of the Dynamic Nuclear Polarization (DNP) of \si{} nuclei in silicon crystals of natural abundance doped with As in the temperature range 0.1-1 K and in strong magnetic field of 4.6 T. This ensures very high degree of electron spin polarization, extremely slow nuclear relaxation and optimal conditions for realization of Overhauser and resolved solid effects. We found that the solid effect DNP leads to an appearance of a pattern of holes and peaks in the ESR line, separated by the super-hyperfine interaction between the donor electron and \si{} nuclei closest to the donor. On the contrary, the Overhauser effect DNP mainly affects the remote \si{} nuclei having the weakest interaction with the donor electron. This leads to an appearance of a very narrow ($\approx$ 3 mG wide) hole in the ESR line. We studied relaxation of the holes after burning, which is caused by the nuclear spin diffusion. Analyzing the spin diffusion data with a simple one-dimensional spectral diffusion model leads to a value of the spectral diffusion coefficient $D=8(3)\times 10^{-3}$ mG$^2$/s. Our data indicate that the spin diffusion is not completely prevented even in the frozen core near the donors. The emergence of the narrow hole after the Overhauser DNP may be explained by a partial "softening" of the frozen core caused by Rabi oscillations of the electron spin.