# Plasmonic nanocavity-enabled universal detection of layer-breathing vibrations in two-dimensional materials

## TL;DR

This paper introduces a new method using plasmonic nanocavities to detect hidden layer-breathing vibrations in 2D materials, enabling better understanding of their interfacial interactions.

## Contribution

A universal plasmon-enhanced Raman spectroscopy strategy using nanocavities to detect weak or inactive layer-breathing vibrations in 2D materials.

## Key findings

- Plasmonic nanocavities enhance and detect layer-breathing modes in multilayer graphene and hBN.
- The method modifies polarization selection rules of layer-breathing vibrations.
- An electric-field-modulated model explains intensity profiles and interfacial polarizability modulation.

## Abstract

Conventional Raman spectroscopy faces inherent limitations in detecting interlayer layer-breathing (LB) vibrations with inherently weak electron-phonon coupling or Raman inactivity in two-dimensional materials, hindering insights into interfacial coupling and stacking dynamics. Here, we demonstrate a universal plasmon-enhanced Raman spectroscopy strategy using gold or silver nanocavities to strongly enhance and detect LB modes in multilayer graphene, hBN, and their van der Waals heterostructures. Plasmonic nanocavities even modify the linear and circular polarization selection rules of the LB vibrations. By developing an electric-field-modulated interlayer bond polarizability model, we quantitatively explain the observed intensity profiles and reveal the synergistic roles of localized plasmonic field enhancement and interfacial polarizability modulation. This model successfully describes the behavior of plasmon-enhanced LB vibrations across different material systems and nanocavity geometries. This work not only overcomes traditional detection barriers but also provides a quantitative framework for probing interlayer interactions, offering a versatile platform for investigating hidden interfacial phonons and advancing the characterization of layered quantum materials.

Plasmonic nanocavities enable universal detection of layer-breathing modes in two-dimensional materials via plasmon-enhanced Raman spectroscopy, overcoming the limit of weak electron-phonon coupling or Raman inactivity, and delivering a quantitative framework for interlayer coupling analysis.