# Local photo-excitation of shift current in noncentrosymmetric systems

## TL;DR

This paper theoretically demonstrates that local photo-excitation in noncentrosymmetric materials can induce a shift current independent of excitation position or system size, highlighting its potential for efficient photovoltaic devices.

## Contribution

It introduces a theoretical model showing local photo-excitation can generate shift current regardless of excitation location or system length, unlike conventional photocurrent.

## Key findings

- Shift current is independent of excitation position and system size.
- Local photo-excitation can induce a persistent shift current.
- Contrast with conventional photocurrent suppression at local excitation.

## Abstract

Photocurrent in solids is an important phenomenon with many applications including the solar cells. In conventional photoconductors, the electrons and holes created by light irradiation are separated by the external electric field, resulting in a current flowing into electrodes. Shift current in noncentrosymmetric systems is distinct from this conventional photocurrent in the sense that no external electric field is needed, and, more remarkably, is driven by the Berry phase inherent to the Bloch wavefunction. It is analogous to the polarization current in the ground state but is a d.c. current continuously supported by the nonequilibrium steady state under the pumping by light. Here we show theoretically, by employing Keldysh-Floquet formalism applied to a simple one-dimensional model, that the local photo excitation can induce the shift current which is independent of the position and width of the excited region and also the length of the system. This feature is in stark contrast to the conventional photocurrent, which is suppressed when the sample is excited locally at the middle and increases towards the electrodes. This finding reveals the unconventional nature of shift current and will pave a way to design a highly efficient photovoltaic effect in solids.