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Ultrafast charge ordering by self-amplified exciton-phonon dynamics in TiSe2
Chao Lian1, Sheng-Jie Zhang1, Shi-Qi Hu1
1Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, P. R. China.
Nature Communications
|January 4, 2020
Summary
Charge density waves (CDWs) in TiSe2 arise from separated exciton and lattice dynamics. Laser pulses initiate electronic changes, followed by electron-phonon coupling, amplifying CDW ordering.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Mechanics
Background:
- The origin of charge density waves (CDWs) in TiSe2 remains debated.
- Difficulty in distinguishing excitonic pairing and electron-phonon coupling (EPC) timescales.
Purpose of the Study:
- To resolve the interplay between ultrafast exciton and periodic lattice distortion (PLD) dynamics in TiSe2.
- To elucidate the microscopic mechanism behind CDW formation.
Main Methods:
- Real-time time-dependent density functional theory (TDDFT) simulations.
- Analysis of ultrafast exciton and PLD dynamics.
- Comparison with photoemission experimental data.
Main Results:
- Laser pulses induce a rapid bonding-antibonding transition within 20 fs, disrupting exciton order.
- Weakened electronic order triggers ionic movements antiparallel to original PLD.
- Electron-phonon coupling (EPC) amplifies these processes, leading to CDW ordering inversion.
Conclusions:
- A clear separation of exciton and PLD dynamics was achieved.
- The study resolves the key initial processes governing CDW dynamics in TiSe2.
- Findings provide a microscopic understanding of CDW formation mechanisms.
