Electrochemically Tunable Magneto-Optical Chirality Enables Dynamic Manipulation of Exciton Polarization in Plasmonic Semiconductor Nanocrystals

Plasmonic semiconductor nanocrystals could enable internal coupling between the localized surface plasmon and exciton, laying the foundation for various photonic, optoelectronic, and quantum technologies. Although resonant coupling between plasmon and exciton has not been realized, the angular momentum generated by the cyclotron motion of plasmon-related free carriers in an external magnetic field allows for unipolar exciton polarization in degenerately doped semiconductor nanocrystals. However, exploitation of this nonresonant coupling for technological applications requires on-demand manipulation of the carrier angular momentum and the corresponding exciton polarization in a static magnetic field. Here, we demonstrate electrochemical tuning of the excitonic magneto-optical chirality in plasmonic ZnO nanocrystals via small external potentials. Using <i>operando</i> magnetic circular dichroism measurements of spectroelectrochemical cells fabricated from these nanocrystals, we show that energy and intensity of the excitonic magneto-optical signal are strongly dependent on the applied voltage. Our results suggest that only a few electrons injected in a sub-10 nm nanocrystal could lead to a detectable change in the exciton polarization, potentially allowing for single-carrier-induced quantum information processing and sensing in a static magnetic field at room temperature.