Universal Enhancement Effect of Nonlinear Optical Response from Band Hybridization

Bulk photovoltaic effect, i.e. shift current, is a nonlinear second‐order optical response that can rectify an alternating current (AC) electric field into a direct current (DC). Depending on the wavelength of the incident light, shift current finds applications in various fields, including solar energy conversion and radiation detection. Its promising application in energy conversion and information processing has inspired investigations to uncover the relationship between shift current and electronic structures of materials. Despite numerous efforts dedicated to designing principles for strong bulk photovoltaic effect materials, the only widely accepted crucial parameter is the joint density of states (JDOS). In this study, employing effective model analysis and first‐principles calculations, an enhancement effect of bulk photovoltaic effect is found to arise from band hybridization that is typically along with anti‐crossing‐like electronic band structures, similar to the Berry curvature effects in intrinsic anomalous Hall conductivity. While this mechanism does not offer a comprehensive understanding of the relationship between electronic structure and the magnitude of bulk photovoltaic effect, it represents practical progress in the design of materials with strong bulk photovoltaic effect.