Spectral dynamics of topological shift-current in ferroelectric semiconductor SbSI

TL;DR

This study investigates the ultrafast dynamics of shift current in ferroelectric SbSI, revealing how Berry connection influences electron behavior and terahertz emission during photoexcitation, with implications for ultrafast optoelectronic devices.

Contribution

It provides the first direct observation of the time evolution of shift current in a ferroelectric semiconductor, highlighting the role of Berry connection in ultrafast electron dynamics.

Findings

Ultrafast shift current dynamics observed via terahertz emission.

Electron cloud swings over sub-picosecond timescale.

Berry connection significantly influences interband optical transitions.

Abstract

Photoexcitation in solids brings about transitions of electrons/holes between different electronic bands. If the solid lacks an inversion symmetry, these electronic transitions support spontaneous photocurrent due to the topological character of the constituting electronic bands; the Berry connection. This photocurrent, termed shift current, is expected to emerge on the time-scale of primary photoexcitation process. We observed ultrafast time evolution of the shift current in a prototypical ferroelectric semiconductor by detecting emitted terahertz electromagnetic waves. By sweeping the excitation photon energy across the band gap, ultrafast electron dynamics as a source of terahertz emission abruptly changes its nature, reflecting a contribution of Berry connection upon interband optical transition. The shift excitation carries a net charge flow, and is followed by a swing-over of the electron cloud on the sub-picosecond time-scale of electron-phonon interaction. Understanding these substantive characters of the shift current will pave the way for its application to ultrafast sensors and solar cells.