Electrically Induced Nuclear Resonance inAl2O3(Ruby)

Abstract

The application of an electric field to a crystalline lattice will, in general, produce an optical mode distortion. This lattice distortion will contribute to the electric field gradient tensor at the positions of the various atoms in the lattice. By applying an oscillating electric field to a single crystal of $\ensuremath{\alpha}$-${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ we have induced $\ensuremath{\Delta}m=\ifmmode\pm\else\textpm\fi{}2$ transitions for the ${\mathrm{Al}}^{27}$ nuclear spins. These "quadrupole" transitions were observed with a nuclear double resonance technique at 4.2\ifmmode^\circ\else\textdegree\fi{}K. An rf electric field orthogonal to the trigonal axis of the crystal induced an oscillating asymmetry parameter $\ensuremath{\eta}$ in the electric field gradient tensor. The magnitude of $\ensuremath{\eta}$ as determined from the transition probability is 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$/(V/cm). The transient behavior as well as the steady-state populations were observed following the application and removal of the rf electric field. The initial slope of the signal following the application of the electric field was used to determine the quadrupole transition probability, and the remaining transient response was interpreted qualitatively in terms of the normal modes of the relaxation. These modes were derived from the rate equations which included the external driving terms. The line shape for the $\ensuremath{\Delta}m=\ifmmode\pm\else\textpm\fi{}2$ nuclear electric resonance was observed indirectly and is more than twice as broad as the dipolar lines with a distinct asymmetry. The width and shape are interpreted in terms of the nuclear dipole-dipole interaction.