Simulations of polaron spin inversion in an organic semiconductor: Comparison of two mechanisms

We present a model study of the effects of two mechanisms, the Rashba spin-orbit coupling and the spin-flip term, on the polaron spin inversion in an organic semiconductor. We find that, while both mechanisms can impact the polaron spin by changing the polaron level from a spin eigenstate to a spin superposition state, substantial difference can be observed in the static and dynamical properties of the polaron. Given the values of model parameters relevant to conjugated polymers, the magnitude of the polaron spin inversion caused by the spin-orbit coupling is much smaller than that by the spin-flip term. When the dynamical properties of the polaron are considered, spin oscillations induced by both mechanisms are observed when the polaron moves along the polymer chain driven by external electric field. Interestingly, the length of the polaron motion during one spin oscillation period remains constant in the case of spin-orbit coupling, while it is enhanced with increasing the driven electric field in the case of spin-flip term, in which larger spin diffusion length and longer spin relaxation time can be expected.