Accessing new types of photocurrents using polarization-shaped excitation pulses

The excitation of exciton resonances in semiconductors with certain polarization-shaped optical pulses reveals the existence of new photocurrents. For resonant excitation of excitons with an optical pulse whose linear polarization is slowly rotating versus time we observe an antisymmetric shift current linked to a second-order nonlinear tensor that is antisymmetric in its last two Cartesian indices. Moreover, for non-resonant excitation of excitons with an elliptically polarized optical pulse whose major and minor axis slowly decreases and increases in time and become minor and major axis, respectively, we observe an additional symmetric shift current being associated with a second-order nonlinear tensor that is symmetric in its last two Cartesian indices. Both of these currents vanish for continuous-wave excitation and, thus, differ from previously known shift currents.