Manifestation of Dipole-Dipole and Quadrupole Interactions in the Correlator Spectrum of Optically Cooled Nuclear Spins of a Bulk n-Gaas Sample

In this work, we measured the correlator spectrum of optically cooled nuclear spin system of a bulk n-GaAs crystal in a zero magnetic field. The resulting spectrum is described by two contours, which can be interpreted as the participation of nuclear spins in two types of interactions. We analyzed the measured spectrum in the model for classical magnetic moments in the GaAs lattice. The analysis showed that the main contribution to the high-frequency part of the spectrum is due to the dipole-dipole interaction, and that to the low-frequency part is due to the quadrupole interaction.