Ultra-confined Propagating Exciton–Plasmon Polaritons Enabled by Cavity-Free Strong Coupling: Beating Plasmonic Trade-Offs

• Published in: Nanoscale research letters Vol. 17; no. 1; p. 109
• Main Authors: Wang, Yipei, Luo, Aoning, Zhu, Chunyan, Li, Zhiyong, Wu, Xiaoqin
• Format: Journal Article
• Language: English
• Published: New York Springer US 18.11.2022; Springer Nature B.V; SpringerOpen
• Subjects: Cavity resonators; Chemistry and Materials Science; Confinement; Coupling; Energy distribution; Excitons; Exciton–plasmon polaritons; Hybrid systems; Hybridization; Materials Science; Metal nanowires; Molecular Medicine; Momentum; Nanochemistry; Nanoscale Science and Technology; Nanotechnology; Nanotechnology and Microengineering; Nanowires; Photons; Plasmonics; Polaritons; Propagation; Strong coupling; Tradeoffs; Transition metal compounds; Transition metal dichalcogenides; Waveguides; Waveguiding; Strong coupling; Transition metal dichalcogenides; Metal nanowires; Exciton–plasmon polaritons; Waveguiding
• ISSN: 1556-276X; 1931-7573; 1556-276X
• DOI: 10.1186/s11671-022-03748-7

Hybrid coupling systems consisting of transition metal dichalcogenides (TMD) and plasmonic nanostructures have emerged as a promising platform to explore exciton–plasmon polaritons. However, the requisite cavity/resonator for strong coupling introduces extra complexities and challenges for waveguiding applications. Alternatively, plasmonic nano-waveguides can also be utilized to provide a non-resonant approach for strong coupling, while their utility is limited by the plasmonic confinement-loss and confinement-momentum trade-offs. Here, based on a cavity-free approach, we overcome these constraints by theoretically strong coupling of a monolayer TMD to a single metal nanowire, generating ultra-confined propagating exciton–plasmon polaritons (PEPPs) that beat the plasmonic trade-offs. By leveraging strong-coupling-induced reformations in energy distribution and combining favorable properties of surface plasmon polaritons (SPPs) and excitons, the generated PEPPs feature ultra-deep subwavelength confinement (down to 1-nm level with mode areas ~ 10 –4 of λ 2 ), long propagation length (up to ~ 60 µm), tunable dispersion with versatile mode characters (SPP- and exciton-like mode characters), and small momentum mismatch to free-space photons. With the capability to overcome the trade-offs of SPPs and the compatibility for waveguiding applications, our theoretical results suggest an attractive guided-wave platform to manipulate exciton–plasmon interactions at the ultra-deep subwavelength scale, opening new horizons for waveguiding nano-polaritonic components and devices.