Real-Space Plasmon Imaging Reveals Modified Electronic Structure of Gold at the Monolayer Limit

TL;DR

This study demonstrates that monolayer gold exhibits metallic properties similar to bulk gold, with unique plasmonic behavior, opening new avenues for nanoscale photonics and electronics.

Contribution

First optical characterization of a stable gold monolayer showing its 2D metallic nature and plasmonic properties using nanoimaging and Drude model analysis.

Findings

Gold monolayer supports short-wavelength plasmon-polaritons.

Relaxation time comparable to bulk gold, indicating similar electronic dynamics.

Drude weight nearly twice the bulk value, confirming metallic behavior.

Abstract

Atomically thin materials exhibit electronic and optical properties distinct from their three-dimensional counterparts. For metals, particularly gold, monolayer studies remain largely unexplored due to fabrication and characterisation challenges. Here we report the first optical study of a stable quasi-freestanding gold monolayer formed by Au intercalation between graphene and SiC. Mid-infrared nanoimaging reveals plasmon-polaritons with wavelengths nearly an order of magnitude shorter than free-space light. Analysis of their dispersion using a Drude model yields a relaxation time of $\tau = 18\,$fs, comparable to bulk gold, and a Drude weight of $D = 1.3\,$mS$\cdot$eV, nearly twice the bulk expectation. These results establish monolayer gold as a two-dimensional metal, opening opportunities for nanoscale photonics, plasmonics and ultra-thin electronics.