[Paper Review] Strong exciton-plasmon coupling in MoS2 coupled with plasmonic lattice

Wenjing Liu, Bumsu Lee+5 more|arXiv (Cornell University)|Nov 12, 2015

Advanced biosensing and bioanalysis techniques18 citations

TL;DR

This study demonstrates strong exciton-plasmon coupling in a monolayer MoS2 integrated with a silver nanodisk array plasmonic lattice, achieving a coupling strength of up to 58 meV at 77 K and retaining it at room temperature. The coupling arises from the hybridization of MoS2 excitons, localized surface plasmon resonances (LSPRs), and lattice resonances, with tunable polaritonic properties via geometric engineering of the plasmonic lattice.

ABSTRACT

We demonstrate strong exciton-plasmon coupling in silver nanodisk arrays integrated with monolayer MoS2 via angle-resolved reflectance microscopy spectra of the coupled system. Strong exciton-plasmon coupling is observed with the exciton-plasmon coupling strength up to 58 meV at 77 K, which also survives at room temperature. The strong coupling involves three types of resonances: MoS2 excitons, localized surface plasmon resonances (LSPRs) of individual silver nanodisks and plasmonic lattice resonances of the nanodisk array. We show that the exciton-plasmon coupling strength, polariton composition and dispersion can be effectively engineered by tuning the geometry of the plasmonic lattice, which makes the system promising for realizing novel two-dimensional plasmonic polaritonic devices.

Motivation & Objective

• To achieve strong coupling between excitons in monolayer MoS2 and plasmonic modes in a structured silver nanodisk array.
• To investigate the interplay of three resonant modes: MoS2 excitons, localized surface plasmon resonances (LSPRs), and plasmonic lattice resonances.
• To demonstrate tunability of the coupling strength, polariton composition, and dispersion through geometric engineering of the plasmonic lattice.
• To enable the design of novel two-dimensional plasmonic polaritonic devices with enhanced light-matter interaction.

Proposed method

• Angle-resolved reflectance microscopy was used to probe the optical response of the MoS2-plasmonic lattice heterostructure.
• Monolayer MoS2 was mechanically exfoliated and transferred onto a periodic array of silver nanodisks.
• The plasmonic lattice was fabricated using electron-beam lithography and metal evaporation to define nanodisk arrays with tunable periodicity and geometry.
• The system's reflectance spectra were measured at varying angles and temperatures (77 K and room temperature) to identify vacuum Rabi splitting and coupling strength.
• Theoretical modeling was used to identify and assign the three resonant modes: MoS2 excitons, LSPRs of individual nanodisks, and collective lattice resonances.
• Geometric parameters such as nanodisk size, spacing, and lattice periodicity were systematically varied to tune the coupling strength and polariton dispersion.

Experimental results

Research questions

• RQ1 Can strong exciton-plasmon coupling be achieved in a two-dimensional MoS2-plasmonic lattice heterostructure?
• RQ2 What are the contributions of individual LSPRs, collective lattice resonances, and MoS2 excitons to the observed coupling?
• RQ3 To what extent can the coupling strength and polariton dispersion be engineered through geometric tuning of the plasmonic lattice?
• RQ4 Does strong coupling persist at room temperature, enabling practical device operation?
• RQ5 How do the three resonant modes (excitons, LSPRs, lattice resonances) hybridize to form polaritonic states?

Key findings

• Strong exciton-plasmon coupling was experimentally observed with a coupling strength of up to 58 meV at 77 K, confirmed by vacuum Rabi splitting in reflectance spectra.
• The coupling strength remains significant at room temperature, indicating robustness for practical applications.
• Three distinct resonant modes—MoS2 excitons, individual nanodisk LSPRs, and collective lattice resonances—were identified and shown to hybridize into polaritonic states.
• The polariton dispersion and composition were controllably tuned by varying the geometry of the plasmonic lattice, including nanodisk size and array periodicity.
• Angle-resolved measurements revealed clear anticrossing behavior, confirming the formation of hybridized exciton-plasmon polaritons.
• The system supports tunable, strong light-matter interaction in a two-dimensional platform, enabling design of novel polaritonic devices.