Non-thermal separation of electronic and structural orders in a persisting charge density wave

Area of Science:

• Condensed Matter Physics
• Materials Science
• Ultrafast Spectroscopy

Background:

• Complex materials exhibit spontaneous symmetry-breaking transitions with intricate couplings between different degrees of freedom.
• Observing the interplay between electronic and lattice dynamics on femtosecond timescales has been a significant challenge.
• Existing ultrafast techniques often probe electronic or lattice dynamics separately, hindering simultaneous observation of multiple orders.

Discussion:

• This study introduces ultrabroadband terahertz pulses as a tool to simultaneously track the ultrafast evolution of coexisting lattice and electronic orders.
• The charge density wave (CDW) in 1T-TiSe2 was investigated, revealing distinct responses of its excitonic correlations and periodic lattice distortion (PLD) components to optical excitation.
• The persistence of the PLD even after quenching of the excitonic order challenges the notion that excitonic correlations are the sole driver of the CDW transition.

Key Insights:

• Terahertz pulses enable simultaneous femtosecond-scale observation of coupled order parameters.
• Excitonic correlations and periodic lattice distortions in 1T-TiSe2 exhibit differential ultrafast dynamics.
• The findings demonstrate that excitonic correlations are not the sole driving force behind the charge density wave transition in this material.

Outlook:

• This technique provides profound insights into disentangling strongly coupled order parameters in the time domain.
• It offers a new avenue for understanding a broad class of symmetry-breaking phase transitions in complex materials.
• Future research can apply this method to other systems exhibiting coupled orders, such as unconventional superconductors and colossal magnetoresistance materials.