Invited
Shift and ballistic currents from first principles

Interest in sustainable energy motivates study of the bulk photovoltaic effect (BPVE). We outline an automated method to design distortions that enhance the shift current BPVE of monolayer MoS and use it to uncover a polar distortion that increases the integrated shift current more than ten-fold. Because the distortion can be driven by a static electric field via the converse piezoelectric effect, this finding shows that electric fields can be used to engineer the shift current response of a material and complements previous work showing that mechanical strain can also modulate the shift current response.

The ab initio methods commonly used to model the BPVE include only the shift current contribution to the BPVE. To overcome this deficiency, we present a method that enables the ballistic current—a current resulting from asymmetric scattering—from first principles. We use a perturbative approach to express the ballistic current due to electron-phonon and electron-hole scattering and calculate the ballistic current for BaTiO from first principles. The current due to electron-phonon scattering is comparable to the shift current, and is therefore experimentally relevant, while the current due to electron-hole scattering is much smaller in magnitude. This methodological development enables closer agreement between theory and experiments and lays the groundwork for further prediction and design of materials with large BPVE.