Control of the Exciton Radiative Lifetime in van der Waals Heterostructures

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Atomically thin transition metal dichalcogenides exhibit strong excitonic effects with large oscillator strengths.
• Encapsulating these materials in hexagonal boron nitride (hBN) narrows optical transitions, approaching homogeneous exciton linewidths.

Purpose of the Study:

• To investigate the tunability of exciton radiative rates in van der Waals heterostructures.
• To explore the influence of hexagonal boron nitride (hBN) encapsulation layer thickness on exciton dynamics.
• To understand the role of electrodynamical effects, specifically the Purcell effect, on exciton recombination.

Main Methods:

• Fabrication of van der Waals heterostructures using transition metal dichalcogenide monolayers encapsulated in hexagonal boron nitride (hBN) of varying thicknesses.
• Time-resolved photoluminescence measurements to probe exciton spontaneous emission times.
• Theoretical calculations of exciton recombination rates in the weak exciton-photon coupling regime.

Main Results:

• Exciton radiative rates in MoSe_{2}/hBN heterostructures are tunable by altering the hBN layer thickness.
• Spontaneous emission times of neutral excitons can be modified by up to an order of magnitude, reaching up to 10 ps.
• Observed radiative decay rate enhancements are consistent with theoretical predictions based on the Purcell effect.

Conclusions:

• The Purcell effect significantly influences exciton radiative recombination in hBN-encapsulated transition metal dichalcogenides.
• Controlling hBN thickness provides a method to tailor exciton dynamics and optical properties.
• This understanding is crucial for elucidating relaxation and recombination mechanisms of both neutral and charged excitons.