Real-space obstruction control of the shift current in two-dimensional Quantum Spin Hall insulators

Abstract

The search for materials exhibiting a large bulk photovoltaic effect has recently expanded to low-band-gap systems capable of operating in the infrared regime, with potential applications in optoelectronics. Among the microscopic mechanisms contributing to this phenomenon, the shift current is one of the dominant sources of photocurrent generation. Owing to its geometric origin, the shift current is not only determined by the optical transition probability but also by the real-space displacement associated with the optical excitation, making non-centrosymmetric materials with obstructed electronic wave functions particularly promising candidates. In this work, using a tight-binding model of a quantum spin Hall insulator on a triangular lattice, we investigate the nonlinear photocurrent across trivial, quantum spin Hall, and higher-order topological insulating phases. We show that obstructed topological phases exhibit a substantially enhanced shift-current response, despite the similar electronic band structure. We identify the origin of this enhancement in optical transitions between states belonging to distinct Wannier-center sectors, which allow for a large real-space displacement upon photoexcitation and, depending on the topological phase, control the sign of the shift current. Our results extend the search for controllable bulk photovoltaic effects to materials characterized by real-space electronic obstruction and identify indenene, a monolayer of In on SiC(0001), as a promising candidate for realizing this phenomenon.