Spectral dynamics of shift current in ferroelectric semiconductor SbSI

Area of Science:

• Solid-state physics
• Materials science
• Quantum mechanics

Background:

• Photoexcitation in solids causes electron/hole transitions between electronic bands.
• Solids lacking inversion symmetry exhibit spontaneous photocurrent due to the Berry connection, known as shift current.
• Shift current is expected to occur on the ultrafast timescale of photoexcitation.

Purpose of the Study:

• To observe and understand the ultrafast dynamics of shift current in a ferroelectric semiconductor.
• To investigate the role of the Berry connection in interband optical transitions and photocurrent generation.
• To explore potential applications of shift current in ultrafast technologies.

Main Methods:

• Ultrafast time-resolved terahertz (THz) electromagnetic wave emission spectroscopy.
• Excitation photon energy was swept across the bandgap of antimony sulfur iodide (SbSI).
• First-principles calculations were employed to understand the observed phenomena.

Main Results:

• Ultrafast evolution of shift current was observed in SbSI on a subpicosecond timescale.
• The nature of ultrafast electron dynamics, a source of THz emission, changed abruptly with excitation photon energy.
• Evidence of the Berry connection's contribution to interband optical transitions and net charge flow was detected.
• A rapid swing of the electron cloud following shift excitation was observed.

Conclusions:

• The study reveals the ultrafast nature and underlying mechanisms of shift current in ferroelectric semiconductors.
• The Berry connection plays a crucial role in generating photocurrent in non-centrosymmetric materials.
• Understanding shift current dynamics is key for developing next-generation ultrafast sensors and solar cells.