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 λ²), 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.

由过渡金属二硫化物 (TMD) 和等离子体纳米结构组成的混合耦合系统已成为探索激子-等离子体激元的有前途的平台。然而，强耦合所必需的空腔/谐振器给波导应用带来了额外的复杂性和挑战。或者，等离子体纳米波导也可用于为强耦合提供非共振方法，而它们的效用受到等离子体限制损失和限制动量权衡的限制。在这里，基于无腔方法，我们通过单层 TMD 与单金属纳米线的理论上的强耦合克服了这些限制，产生了超限制传播激子-等离子体激元 (PEPP)，击败了等离子体权衡。^–4 of λ ²）、长传播长度（高达 ~ 60 µm）、具有多种模式特征（SPP 和类激子模式特征）的可调谐色散，以及与自由空间光子的小动量失配。由于能够克服 SPP 的权衡和波导应用的兼容性，我们的理论结果表明一个有吸引力的导波平台可以在超深亚波长尺度上操纵激子 - 等离子体激元相互作用，为波导纳米极化激子开辟新视野组件和设备。