Strong isotopic effect in the electron-mediated nuclear-nuclear interaction in solids

Abstract

We studied the nuclear-nuclear spin interaction mediated by an unpaired electron spin, focusing on an isotopic effect by electron nuclear double resonance (ENDOR) spectroscopy. We investigated a linear cluster Ga-Ti3+-Ga in titanium-doped gallium oxyde β − Ga2O3, whereby the unpaired electron spin density of Ti3+ is equally delocalized on the nuclear spins I = 3/2 of nearest-neighboring 69Ga and 71Ga nuclei. The linear geometry of the spin arrangement allowed us to easily identify the ENDOR spectra for the three possible isotopic configurations: 69Ga-Ti-71Ga 69Ga-Ti-69Ga and 71Ga-Ti-71Ga. Despite the magnetic moments of 71Ga and 69Ga nuclei differing by only by 27%, the experimental effect of the electron-mediated nuclear-nuclear interaction (pseudodipolar interaction) on the ENDOR spectra is one order of magnitude larger ( 1 MHz) for the symmetrical clusters (69Ga-Ti-69Ga and 71Ga-Ti-71Ga, respectively) than for the asymmetrical cluster 69Ga-Ti-71Ga (<0.1 MHz). This important isotopic effect in the internuclear interaction is a consequence of the cluster symmetry with a local inversion center for the symmetrical configurations, which is lacking in the asymmetrical configuration. These symmetrical clusters thus combine a resolved nuclear-nuclear spin interaction, a nuclear spin monitoring by an unpaired electron, and a large nuclear spin quantum register, which make them attractive for quantum information processing whereby nuclear qubits can be monitored by short selective radiofrequency pulses.