Twist Angle Dependent Interlayer Exciton Lifetimes in van der Waals Heterostructures

TL;DR

This study demonstrates how the twist angle in van der Waals heterostructures significantly influences interlayer exciton lifetimes, revealing a tunable mechanism for controlling exciton dynamics with potential applications in optoelectronics.

Contribution

It provides a combined experimental and theoretical analysis of how twist angle affects exciton lifetimes, introducing a new dimension for exciton control in twistronics.

Findings

Interlayer exciton lifetimes vary by an order of magnitude with twist angle.

Theoretical separation of mechanisms affecting exciton radiative lifetimes.

Predicted temperature dependence of exciton lifetimes varies with twist angle.

Abstract

In van der Waals (vdW) heterostructures formed by stacking two monolayers of transition metal dichalcogenides, multiple exciton resonances with highly tunable properties are formed and subject to both vertical and lateral confinement. We investigate how a unique control knob, the twist angle between the two monolayers, can be used to control the exciton dynamics. We observe that the interlayer exciton lifetimes in $\text{MoSe}_{\text{2}}$/$\text{WSe}_{\text{2}}$ twisted bilayers (TBLs) change by one order of magnitude when the twist angle is varied from 1$^\circ$ to 3.5$^\circ$. Using a low-energy continuum model, we theoretically separate two leading mechanisms that influence interlayer exciton radiative lifetimes. The shift to indirect transitions in the momentum space with an increasing twist angle and the energy modulation from the moir\'e potential both have a significant impact on interlayer exciton lifetimes. We further predict distinct temperature dependence of interlayer exciton lifetimes in TBLs with different twist angles, which is partially validated by experiments. While many recent studies have highlighted how the twist angle in a vdW TBL can be used to engineer the ground states and quantum phases due to many-body interaction, our studies explore its role in controlling the dynamics of optically excited states, thus, expanding the conceptual applications of "twistronics".