Effect of exchange coupling on coherently controlled spin-dependent transition rates

The effect of exchange interactions within spin pairs on spin-dependent transport and recombination rates through localized states in semiconductors during coherent electron-spin resonant excitation is studied theoretically. It is shown that for identical spin systems, significant quantitative differences are to be expected between the results of pulsed electrically/optically detected magnetic resonance (pEDMR/pODMR) experiments, where permutation symmetry is the observable, and the results of pulsed electron-spin resonance (pESR) experiments, with polarization in the x-y plane of the rotating frame as the observable. It is predicted that beat oscillations of the spin nutations and not the nutations themselves dominate the transport or recombination rates when the exchange coupling strength or the field strength of the exciting radiation exceed the difference between the Zeeman energies within the spin pair. Furthermore, while the intensities of the rate oscillations decrease with increasing exchange within the spin pairs, the singlet and triplet signals retain their relative strengths. This means that pEDMR and pODMR experiments allow experimental access to ESR forbidden singlet transitions.