Two-dimensional materials exhibit a fascinating range of electronic and photonic properties vital for nanophotonics, quantum optics and emerging quantum information technologies. Merging concepts from the fields of ab initio materials science and nanophotonics, there is now an opportunity to engineer new photonic materials whose optical, transport, and scattering properties are tailored to attain thermodynamic and quantum limits. Here, we present first-principles calculations predicting that Argentene, a single-crystalline hexagonal close-packed monolayer of Ag, can dramatically surpass the optical properties and electrical conductivity of conventional plasmonic materials. In the low-frequency limit, we show that the scattering rate and resistivity reduce by a factor of three compared to the bulk three-dimensional metal. Most importantly, the low scattering rate extends to optical frequencies in sharp contrast to e.g. graphene, whose scattering rate increase drastically in the near-infrared range due to optical-phonon scattering. Combined with an intrinsically high carrier density, this facilitates highly-confined surface plasmons extending to visible frequencies. We evaluate Argentene across three distinct figures of merit, spanning the spectrum of typical plasmonic applications; in each, Argentene outperforms the state-of-the-art. This unique combination of properties will make Argentene a valuable addition to the two-dimensional heterostructure toolkit for quantum electronic and photonic technologies.
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