Brightening Interlayer Excitons by Electric-Field-Driven Hole Transfer in Bilayer WSe_{2}

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Optics

Background:

• Interlayer excitons in bilayer transition metal dichalcogenides (TMoDCs) are crucial for optoelectronic applications.
• Understanding the optical properties of these excitons, particularly their brightness, is essential for device design.
• Conventional models struggle to explain the brightness of interlayer excitons when energetically separated from intralayer excitons.

Purpose of the Study:

• Investigate the origin of optical brightness in interlayer excitons in bilayer WSe2 under electric fields.
• Determine the role of electric fields and inter-/intralayer exciton interactions in modulating exciton properties.
• Identify mechanisms responsible for enhancing oscillator strength in interlayer excitons.

Main Methods:

• Optical spectroscopy: Employed reflectance contrast spectroscopy to observe interlayer excitons (A_{1s}^{I}, A_{2s}^{I}, B_{1s}^{I}) in bilayer WSe2.
• Computational modeling: Utilized density functional theory (DFT) calculations to analyze electronic band structure and wave function behavior.
• Theoretical analysis: Developed models to explain exciton behavior under applied electric fields.

Main Results:

• Observed optically bright interlayer excitons in bilayer WSe2 under applied electric fields.
• DFT calculations revealed that electric fields distort valence-band states, causing interlayer hole transfer.
• This field-induced hole transfer imparts intralayer character, enhancing oscillator strength without significant hybridization.
• Simulations confirmed interlayer hole transfer as the dominant brightening mechanism.

Conclusions:

• Interlayer hole transfer is identified as the primary mechanism for brightening interlayer excitons in bilayer TMoDCs.
• This mechanism is particularly effective when interlayer and intralayer excitons are energetically well separated.
• The findings provide new insights into controlling exciton properties in 2D materials for advanced electronic and photonic devices.