  An AC electric field applied to a donor-bound electron in a semiconductor
modulates the orbital character of its wave function, which affects the
electron's spin dynamics via the spin-orbit interaction. Numerical calculations
of the spin dynamics of a hydrogenic donor (Si) embedded in GaAs, using a
real-space multi-band k.p formalism, show the high symmetry of the hydrogenic
donor state results in strongly nonlinear dependences of the electronic g
tensor on applied fields. A nontrivial consequence is that the most rapid Rabi
oscillations occur for electric fields modulated at a subharmonic of the Larmor
frequency.
