Unusual Exciton-Phonon Interactions at van der Waals Engineered Interfaces

TL;DR

This paper uncovers a novel Raman scattering process at van der Waals interfaces, revealing enhanced phonon interactions and exciton coupling, which could impact the design of future optoelectronic devices.

Contribution

It demonstrates a new interfacial Raman scattering mechanism in vdW heterostructures, with amplified signals via resonant phonon-exciton coupling, and highlights the importance of interface geometry.

Findings

Enhanced Raman signals at vdW interfaces with specific materials.

Resonant coupling amplifies Raman scattering by nearly two orders of magnitude.

Interfacial Raman scattering varies with heterostructure geometry.

Abstract

Raman scattering is a ubiquitous phenomenon in light-matter interactions which reveals a material's electronic, structural and thermal properties. Controlling this process would enable new ways of studying and manipulating fundamental material properties. Here, we report a novel Raman scattering process at the interface between different van der Waals (vdW) materials as well as between a monolayer semiconductor and 3D crystalline substrates. We find that interfacing a WSe2 monolayer with materials such as SiO2, sapphire, and hexagonal boron nitride (hBN) enables Raman transitions with phonons which are either traditionally inactive or weak. This Raman scattering can be amplified by nearly two orders of magnitude when a foreign phonon mode is resonantly coupled to the A exciton in WSe2 directly, or via an A'1 optical phonon from WSe2. We further showed that the interfacial Raman scattering is distinct between hBN-encapsulated and hBN-sandwiched WSe2 sample geometries. This cross-platform electron-phonon coupling, as well as the sensitivity of 2D excitons to their phononic environments, will prove important in the understanding and engineering of optoelectronic devices based on vdW heterostructures.