Nanoscale charge control is a key enabling technology in plasmonics, electronic band structure engineering, and the topology of two-dimensional materials. By exploiting the large electron affinity of α-RuCl 3 , we are able to visualize and quantify massive charge transfer at graphene/α-RuCl 3 interfaces through generation of chargetransfer plasmon polaritons (CPPs). We performed nanoimaging experiments on graphene/α-RuCl 3 at both ambient and cryogenic temperatures and discovered robust plasmonic features in otherwise ungated and undoped structures. The CPP wavelength evaluated through several distinct imaging modalities offers a high-fidelity measure of the Fermi energy of the graphene layer: E F = 0.6 eV (n = 2.7 × 10 13 cm −2 ). Our first-principles calculations link the plasmonic response to the work function difference between graphene and α-RuCl 3 giving rise to CPPs. Our results provide a novel general strategy for generating nanometer-scale plasmonic interfaces without resorting to external contacts or chemical doping.
Natural hyperbolic materials with dielectric permittivities of opposite sign along different principal axes can confine long-wavelength electromagnetic waves down to the nanoscale, well below the diffraction limit. This has been demonstrated using hyperbolic phonon polaritons (HPP) in hexagonal boron nitride (hBN) and -MoO 3 , among other materials. However, HPP dissipation at ambient conditions is substantial and its fundamental limits remain unexplored 1,2 . Here, we exploit cryogenic nano-infrared imaging to investigate propagating HPP in isotopically pure hBN and naturally abundant -MoO 3 crystals. Close to liquid-nitrogen temperatures, the losses for HPP in isotopic hBN drop significantly, resulting in propagation lengths in excess of 25 micrometers, with lifetimes exceeding 5 picoseconds, thereby surpassing prior reports on such highly-confined polaritonic modes.Our nanoscale, temperature-dependent imaging reveals the relevance of acoustic phonons in hyperbolic polariton damping and will be instrumental in mitigating such losses for miniaturized middle infrared technologies operating at the liquid-nitrogen temperatures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.