Shift Current: Quantum Mechanical Picture of the Bulk Photovoltaic Effect

Abstract

When a photon induces an interband transition in a solid, the excited electron (hole) experiences a spatial shift if the crystal lacks an inversion symmetry, leading to a generation of directional photocurrent. This phenomenon has been known as bulk or anomalous photovoltaic effect for years, and is recently reformulated with the viewpoint of quantum mechanics as the change in the geometrical phase upon photoexcitation. It is also predicted that this so-called shift current of electron (hole) can be less-dissipative and ultrafast. We demonstrate the emergence of shift current in several organic and inorganic ferroelectrics by using extensive optical spectroscopies, whose excitation spectra nicely compared to the ones from first-principles band calculations.