Coherence control of directional nonlinear photocurrent in spatially symmetric systems

The interplay between crystal symmetry and its optical responses is at the heart of tremendous recent advances in light-matter interactions and applications. Nonlinear optical processes that produce electric currents, for example the bulk photovoltaic (BPV) effect, require inversion-symmetry-broken materials, such as ferroelectrics. In this work, we demonstrate that such BPV current could be generated in centrosymmetric materials with excitation of out-of-equilibrium coherent phonons. This is very different from the generally studied static or thermally excited states. We show that depending on the coherent phonon phase factor, the photoconductivity contains a static zero-frequency component, as well as THz frequency components. This indicates that a unidirectional current may emerge under synergistic effects of atomic vibration and light irradiation. We also generalize the conventional injection charge current into angular momentum (spin and orbital) degrees of freedom, and demonstrate spin and orbital BPV photoconductivities under coherent phonons. Our findings open the pathway to exploring the exotic phonon-photon-electron coherent interactions in quantum materials.