Gate Tunable Dark Trions in Monolayer WSe_{2}.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Monolayer transition metal dichalcogenides (TMDs) like WSe_{2} exhibit unique excitonic properties.
• Understanding dark excitons and trions is crucial for advanced quantum applications.
• Previous studies have focused on bright excitons, leaving dark exciton physics less explored.

Purpose of the Study:

• To investigate the physics of dark excitons and trions in ultraclean monolayer WSe_{2}.
• To characterize the optical and spin properties of dark trions.
• To explore the tunability of dark trions using electrostatic gating.

Main Methods:

• Fabrication of ultraclean monolayer WSe_{2} devices encapsulated by hexagonal boron nitride (hBN).
• Photoluminescence spectroscopy to detect dark and bright excitons and trions.
• Application of electrostatic gating to tune trion properties.
• Zeeman splitting measurements under a magnetic field to determine spin configuration and valley optical emission.

Main Results:

• Observed and characterized photoluminescence from dark excitons and trions in monolayer WSe_{2}.
• Demonstrated continuous tuning of dark trions between negative and positive states via electrostatic gating.
• Revealed the spin-triplet configuration and distinct valley optical emission of dark trions.
• Measured dark trion binding energies (14-16 meV), lower than bright trions (21-35 meV).
• Found significantly longer dark trion lifetimes (∼1.3 ns) compared to bright trions (∼10 ps), tunable between 0.4-1.3 ns.

Conclusions:

• Dark trions in monolayer WSe_{2} are optically detectable, robust, and gate-tunable.
• Their long lifetimes and tunable nature suggest potential for realizing trion transport in 2D materials.
• This work opens new avenues for exploring dark exciton physics and developing novel quantum devices.