Helicity-dependent optical modulation of polaron spin current in organic semiconductors

The optical response of the transmitting polaron in p-conjugated organic semiconductor to the circularly polarized pulse is theoretically studied. Depending on the helicity of the circularly polarized light, polaron spin flip is achieved within femtoseconds without applying magnetic field, leading to the spin polarization of the polaron current. The magnitude of spin polarization can be modulated by tuning the frequency and amplitude of the circularly polarized light. Furthermore, we demonstrate that the conversions between spin-depolarization and spin -polarization of the polaron current can be repeatedly triggered by applying a series of circularly polarized pulses until the polaron dissociates. Our work suggests a new prospect for all-optically controlling spin current in the organic spintronic devices.