Abstract
We study theoretically the spectrum (s) of spin-dependent transition rates within dipolar and exchange coupled pairs of two spins with undergoing Rabi oscillations due to a coherent magnetic-resonant excitation. We show that the Rabi oscillation controlled rates exhibit a spectrum with three frequency components. When exchange is stronger than the driving field (in the frequency units), the frequency components of the Rabi oscillation do not depend on , rather they are determined by the relation between the and . We derive analytical expressions for the frequencies and the intensities of all three Rabi oscillation components as functions of and , where is detuning of the driving ac field from the Larmor frequency. When , the two lower frequencies approach , while the upper line approaches . Disorder of the local Larmor frequencies leads to a Gaussian broadening of the spectral lines. We calculate corresponding widths for different and . Unexpectedly, we find that one of the frequency components exhibits an unusual evolution with : its frequency decreases with at . Upon further increase of , this frequency then passes through a minimum and, eventually, approaches . Nonmonotonic behavior of the frequencies is accompanied by nonmonotonic behavior of the respective oscillation intensity.
- Received 22 October 2012
DOI:https://doi.org/10.1103/PhysRevB.87.165205
©2013 American Physical Society