Lossless propagation of PT graphene plasmons

TL;DR

This paper derives exact conditions for lossless propagation of graphene plasmons by embedding graphene in an active dielectric, enabling long-range, tunable, and lossless plasmonic devices through gain-assisted design.

Contribution

It provides closed-form formulas for the gain needed to achieve lossless and $ ext{PT}$-symmetric graphene plasmon propagation, verified by full-wave simulations.

Findings

Exact gain required for lossless propagation derived

Identification of $ ext{PT}$-symmetry threshold in graphene plasmonics

Demonstration of long-range, tunable, lossless surface plasmons

Abstract

Graphene supports surface plasmon polaritons (SPPs) with extreme field confinement and electrical tunability, but these waves are typically short-lived due to ohmic loss in the sheet. We show that embedding graphene in an active dielectric can counteract this loss and we derive closed-form design rules to do so, based on gain-assisted plasmonics and plasmonic amplification concepts. Specifically, from the full Maxwell model of a conductive sheet we obtain (i) the exact gain required for lossless plasmon propagation, and (ii) a second critical gain that marks the $\mathcal{PT}$-symmetric threshold, the exceptional point separating propagating and forbidden SPP regimes. The formulas are expressed directly in terms of the complex conductivity of graphene and the surrounding media, making them easy to evaluate and implement. We verify the theory with full-wave eigenmode calculations (COMSOL), showing dispersion and attenuation/amplification trends with and without gain for our plasmonic structures, finding a practical route to engineer long-range, tunable, lossless graphene plasmonics and to map/target non-Hermitian operating phases for device design in single- and double- layer graphene surfaces.