Site-selective electron nuclear double resonance in the exchange-narrowed regime of the ESR in conducting solids

Electron nuclear magnetic double resonance on conduction electrons reveals the hyperfine interaction hidden by the fast electron spin exchange. We use d the Overhauser shift technique to investigate the electron spin density o f the conduction band of gallium oxide, beta -Ga2O3. Due to the monoclinic structure, the conduction band of beta -Ga2O3 is anisotropic and it is domi nated by contributions from the two nonequivalent Ga sites. The large quadr upole couplings of the two gallium isotopes Ga-69 and Ga-71 (both with I = 3/2) are completely resolved in our double-resonance experiments. This reso lved quadrupole interaction allows the determination of the electric field gradients at both gallium sites with high precision and high sensitivity. T he resolved quadrupole splitting is the key to the site-selected determinat ion of the hyperfine interaction. The concepts behind these double-resonanc e techniques are rather general and should be applicable in similar semicon ductor systems. (C) 2001 Academic Press.