Intravalley Spin-Flip Relaxation Dynamics in Single-Layer WS₂.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Monolayer transition metal dichalcogenides (TMDs) exhibit spin-split bands due to strong spin-orbit interaction.
• In tungsten-based TMDs, dark excitons have lower energy than bright A excitons, reducing light emission efficiency.
• Electron scattering from upper to lower conduction bands facilitates the transition to dark excitons.

Purpose of the Study:

• To directly measure intravalley spin-flip relaxation dynamics in monolayer tungsten disulfide (1L-WS2).
• To investigate the temperature dependence and underlying mechanisms of spin-flip relaxation.
• To elucidate the role of electron scattering in optoelectronic device performance.

Main Methods:

• Utilizing valley-selective optical selection rules.
• Employing two-color helicity-resolved pump-probe spectroscopy.
• Performing time-dependent ab initio calculations.

Main Results:

• Intravalley spin-flip relaxation in 1L-WS2 occurs on a sub-picosecond timescale.
• The relaxation process is significantly dependent on temperature, suggesting phonon-assisted scattering.
• Ab initio calculations reveal that scattering away from the K point minimum drastically reduces spin-flip time.

Conclusions:

• Spin-flip relaxation dynamics are critical for understanding light emission efficiency in 1L-TMDs.
• Phonon-assisted scattering plays a key role in rapid spin relaxation.
• Device performance is strongly influenced by the occupation of conduction band states away from the minimum.