1210.0948 (R. Glenn et al.)

Analytical study of spin-dependent transition rates within pairs of
dipolar and strongly exchange coupled spins with (S = 1/2) during magnetic
resonant excitation    [PDF]

R. Glenn, M. E. Limes, B. Saam, C. Boehme, M. E. Raikh

We study theoretically the spectrum, F(s), of spin-dependent transition rates within dipolar D and exchange J coupled pairs of two spins with S=1/2 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 Rabi frequency (J>>\Omega_R), the frequency components of the Rabi oscillation do not depend on J, rather they are determined by the relation between \Omega_R and D. We derive analytical expressions for the frequencies and the intensities of all three Rabi oscillation components as functions of \Omega_R/D and \delta/D, where \delta is detuning of the driving ac field from the Larmor frequency. When \Omega_R>>D, the two lower frequencies approach s=\Omega_R, while the upper line approaches s=2\Omega_R. Disorder of the local Larmor frequencies leads to a Gaussian broadening of the spectral lines. We calculate corresponding widths for different \Omega_R/D and \delta/D. Unexpectedly, we find that one of the frequency components exhibits an unusual evolution with \Omega_R: its frequency decreases with \Omega_R at \Omega_RView original: http://arxiv.org/abs/1210.0948