Strain propagation in layered two-dimensional halide perovskites.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Spectroscopy

Background:

• Layered two-dimensional (2D) halide perovskites exhibit coupled structural and electronic properties sensitive to light excitation.
• Understanding nonlinear lattice dynamics in these soft hybrid materials is crucial but remains limited.
• Impulsive light excitation offers a pathway to probe these dynamic responses.

Purpose of the Study:

• To elucidate the intrinsic strain propagation mechanisms in 2D perovskite single crystals.
• To differentiate between thermoelastic (TE) stress and deformation potential (DP) contributions to strain generation.
• To understand the influence of hot carrier cooling and interlayer bonding on strain dynamics.

Main Methods:

• Transient reflection spectroscopy was employed to study strain propagation.
• Brillouin scattering was used for detecting generated strain pulses.
• A two-temperature model was integrated with strain wave propagation analysis.

Main Results:

• Ultrafast photoexcitation generates strain pulses through TE stress and DP interaction.
• Hot carrier cooling significantly influences the modulation amplitude of the strain.
• Weak van der Waals bonds between organic layers reduce out-of-plane lattice stiffness, leading to slow strain propagation.
• Strain propagation velocity was found to be slow due to reduced lattice stiffness.

Conclusions:

• The study clarifies the mechanisms of strain generation and propagation in 2D perovskite single crystals.
• Hot carrier cooling and interlayer bonding are key factors governing lattice dynamics.
• These findings provide fundamental insights into the strain properties of layered perovskites, essential for their technological applications.