Ultrafast switching of persistent electron and hole currents in ring molecules

A circularly polarized laser pulse can induce persistent intra-molecular currents by either exciting or ionizing molecules. These two cases are identified as electron currents and hole currents, respectively, and up to now they have been studied only separately. We report $\mathit{\text{ab}}\mathit{\text{initio}}$ time-dependent density-functional theory (TDDFT) simulations of currents during resonance-enhanced two-photon ionization of benzene, which reveal for the first time that both electron and hole currents can be present simultaneously. By adjusting the intensity of the laser pulse, the balance between the two types of current can be controlled, and the overall sign of the current can be switched. We provide a physical explanation for the effect in terms of complex molecular orbitals which is consistent with the TDDFT simulations.