Absorption of an oscillating magnetic field power at frequencies of nuclear spin-spin interactions in semiconductors

We present a general overview of our previously published experimental and theoretical studies of the power absorption spectra of oscillating magnetic fields by optically cooled nuclear spins in semiconductors of the A$^3$B$^5$ and A$^2$B$^6$ groups. Absorption spectra were measured in zero and also in weak external static magnetic fields using warm-up spectroscopy, which is an analogue of optically detected nuclear magnetic resonance (ODNMR). The experiments were carried out for a deformed bulk $n$-GaAs layer and a CdTe-based heterostructure. It is shown that the shape of the absorption spectra is determined by nuclear spin-spin interactions, which are very different for the selected semiconductor materials. In particular, from a theoretical analysis of experimental spectra it was established that for an $n$-GaAs crystal in the presence of residual deformation, the shape of the absorption spectrum in a zero magnetic field is determined by quadrupole interactions exceeding nuclear spin-spin interactions. For the CdTe heterostructure, it was established that the shape of the spectrum in zero field has a purely spin-spin character, which is confirmed by our proposed model of nuclear spin clusters. For both $n$-GaAs, and CdTe, absorption spectra were measured and analyzed in external static magnetic fields (analogue of NMR), where homonuclear (Zeeman) absorption peaks were found to be modified by the presence of a nuclear quadrupole (for $n$-GaAs) and pure spin-spin (for CdTe) interactions.