Optical Control of Multistage Phase Transition via Phonon Coupling in MoTe_{2}.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Phase transitions in transition metal dichalcogenides (TMDs) are crucial for their electronic properties.
• Understanding the ultrafast dynamics of these transitions is key to controlling material functionalities.
• Molybdenum Ditelluride (MoTe2) exhibits distinct 2H and 1T' phases with different applications.

Purpose of the Study:

• To investigate the temporal dynamics of laser-induced 2H to 1T' phase transition in MoTe2 monolayers.
• To elucidate the underlying electron-phonon interactions and phonon excitation mechanisms.
• To identify intermediate states and pathways during the non-equilibrium phase transformation.

Main Methods:

• Ultrafast spectroscopy to probe temporal evolution.
• Theoretical modeling of electron-phonon coupling.
• Analysis of phonon excitation and relaxation dynamics.

Main Results:

• The phase transition is driven by fundamental electron-phonon interactions.
• An unexpected phonon excitation and coupling pathway linked to photoexcited electron relaxation was identified.
• The transformation proceeds through three substages involving optical to acoustic phonon scattering (A1', E' to LA(M)) on a subpicosecond timescale.
• An intermediate metallic state was observed during the nonadiabatic transition.

Conclusions:

• The study reveals a novel mechanism for laser-driven phase transitions in MoTe2 monolayers.
• Non-equilibrium relaxation of photoexcited electrons plays a critical role in phonon excitation and coupling.
• The findings offer insights into controlling phase transitions for advanced material applications.