Ultrafast Photo-induced Phase Change in SnSe

TL;DR

This study uses time-resolved THz spectroscopy to reveal an ultrafast, non-thermal phase change in SnSe caused by photoexcitation, leading to charge localization and phase segregation.

Contribution

It demonstrates a new ultrafast, non-thermal phase transition in SnSe driven by optical excitation, characterized by distinct transient THz responses.

Findings

Charge localization indicated by Lorentzian-like spectra

Bimodal rise in photoconductivity due to multiple band excitations

Critical fluence causes a phase segregation and band gap collapse

Abstract

Time-resolved multi-terahertz (THz) spectroscopy is used to observe an ultrafast, non-thermal electronic phase change in SnSe driven by interband photoexcitation with 1.55 eV pump photons. The transient THz photoconductivity spectrum is found to be Lorentzian-like, indicating charge localization and phase segregation. The rise of photoconductivity is bimodal in nature, with both a fast and slow component due to excitation into multiple bands and subsequent intervalley scattering. The THz conductivity magnitude, dynamics, and spectra show a drastic change in character at a critical excitation fluence of approximately 6 mJ/cm^2 due to a photo-induced phase segregation and a macroscopic collapse of the band gap.