Strain wave pathway to semiconductor-to-metal transition revealed by time-resolved X-ray powder diffraction

Area of Science:

• Ultrafast material science
• Solid-state physics
• Nanocrystal phase transitions

Background:

• Triggering phase transitions with light is crucial for ultrafast material science.
• Bistable titanium oxide (Ti₃O₅) nanocrystals exhibit semiconducting-to-metal transitions.
• Understanding the dynamics of these transitions is key to controlling material properties.

Purpose of the Study:

• To investigate the mechanism and dynamics of light-induced phase transitions in Ti₃O₅ nanocrystals.
• To elucidate the role of strain waves in the semiconducting-to-metal transition.
• To compare the speed of strain-driven transitions with thermal processes.

Main Methods:

• Femtosecond powder X-ray diffraction to measure time-resolved lattice deformation.
• Monitoring of intra-cell distortions and long-range deformations.
• Development of a simplified elastic model to describe the transition dynamics.

Main Results:

• Strain waves, initiated by electronic and structural precursors, govern the phase transition pathway.
• Picosecond switching occurs concurrently with propagating acoustic wavefronts.
• The transition is significantly faster than thermal diffusion-controlled processes.

Conclusions:

• Strain waves play a critical role in ultrafast phase transitions in Ti₃O₅ nanocrystals.
• Light-induced phase transitions can be driven by coherent strain dynamics, not just thermal effects.
• This provides a pathway for developing novel ultrafast optical switching materials.