Giant gate-tunable bandgap renormalization and excitonic effects in a 2D semiconductor

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Excitonic effects and exciton binding energies are critical for the performance of two-dimensional (2D) semiconductors in photonic and optoelectronic devices.
• Precise control over these properties is essential for realizing the full technological potential of 2D materials.

Purpose of the Study:

• To investigate and demonstrate large excitonic effects in single-layer rhenium diselenide (ReSe2).
• To achieve gate-tunable control over exciton binding energies in monolayer ReSe2.
• To explore the potential for bandgap renormalization and application in advanced optoelectronics.

Main Methods:

• Fabrication of a back-gated graphene device incorporating single-layer ReSe2.
• Utilized scanning tunneling spectroscopy (STS) to measure the quasiparticle electronic bandgap.
• Employed differential reflectance spectroscopy (DRS) to determine the optical bandgap.

Main Results:

• Observed significant excitonic effects in single-layer ReSe2, with a measured exciton binding energy of 520 meV.
• Demonstrated continuous tuning of the electronic bandgap and exciton binding energy by hundreds of meV via electrostatic gating.
• Attributed the tuning to gate-controlled Coulomb interactions from free carriers in the graphene layer.

Conclusions:

• Single-layer ReSe2 exhibits substantial excitonic effects and gate-tunable binding energies.
• Electrostatic gating provides an effective method to control bandgap renormalization and exciton binding energies in 2D semiconductors.
• Findings pave the way for novel applications in tunable optoelectronic devices.