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Charged Biexciton Formation with Many-Body-Induced Valley Polarization in a Monolayer Semiconductor
Qirui Liu1, Ke Wei2,3, Yuxiang Tang2
1College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China.
ACS Nano
|March 28, 2025
Summary
Complex five-body excitonic complexes in WS2 exhibit robust valley polarization, outperforming simpler systems and offering new avenues for valleytronics. This polarization is surprisingly stable against temperature and pump fluence variations.
Area of Science:
- Many-body physics
- Condensed matter physics
- Low-dimensional materials
Background:
- Excitonic complexes are crucial for understanding quasiparticle interactions.
- Valleytronics leverages electron valley properties for electronic devices.
- Previous research focused on simpler few-body systems like excitons and trions.
Purpose of the Study:
- To explore valley dynamics in five-body charged biexcitons (XX-) in monolayer WS2.
- To investigate the stability and persistence of valley polarization in complex excitonic systems.
- To understand the influence of external factors on valley polarization in XX-.
Main Methods:
- Helicity-resolved ultrafast spectroscopy was employed.
- Experiments were conducted on monolayer WS2 at approximately 150 K.
- System dynamics were probed under varying temperature and pump fluence.
Main Results:
- A near-unity degree of valley polarization was observed in XX-.
- Valley polarization persisted significantly longer than the population lifetime.
- Unexpected positive correlations between polarization and external disturbances (temperature, pump fluence) were found.
Conclusions:
- Multibody excitonic complexes, specifically XX-, are stable systems for maintaining valley polarization.
- Suppressed valley-exchange interactions and dual formation mechanisms contribute to XX- stability.
- These findings suggest potential for valleytronic applications utilizing many-body correlations.
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