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Diffraction of light at lateral inhomogenities is a central process in the near-field studies of nanoscale phenomena, especially the propagation of surface waves. Theoretical description of this process is extremely challenging due to breakdown of plane-wave methods. Here, we present and analyze an exact solution for electromagnetic wave diffraction at the linear junction between two-dimensional electron systems (2DES) with dissimilar surface conductivities. The field at the junction is a combination of three components with different spatial structure: free-field component, non-resonant edge component, and surface plasmon-polariton (SPP). We find closed-form expressions for efficiency of photon-to-plasmon conversion by the edge being the ratio of electric fields in SPP and incident wave. Particularly, the conversion efficiency can considerably exceed unity for the contact between metal and 2DES with large impedance. Our findings can be considered as a first step toward quantitative near-field microscopy of inhomogeneous systems and polaritonic interferometry.
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Rapid progress in electrically-controlled plasmonics in solids poses a question about effects of electronic reservoirs on the properties of plasmons. We find that plasmons in electronically open systems [i.e. in (semi)conductors connected to leads] are prone to an additional damping due to charge carrier penetration into contacts and subsequent thermalization. We develop a theory of such lead-induced damping based on kinetic equation with self-consistent electric field, supplemented by microscopic carrier transport at the interfaces. The lifetime of plasmon in electronically open ballistic system appears to be finite, order of conductor length divided by carrier Fermi (thermal) velocity. The reflection loss of plasmon incident on the contact of semi-conductor and perfectly conducting metal also appears to be finite, order of Fermi velocity divided by wave phase velocity. Recent experiments on plasmon-assisted photodetection are discussed in light of the proposed lead-induced damping phenomenon.
An electron beam traversing a structured plasmonic field is shown to undergo diffraction with characteristic angular patterns of both elastic and inelastic outgoing electron components. In particular, a plasmonic {it grating} (e.g., a standing wave formed by two counter-propagating plasmons in a thin film) produces diffraction orders of the same parity as the net number of exchanged plasmons. Large diffracted beam fractions are predicted to occur for realistic plasmon intensities in attainable geometries due to a combination of phase and amplitude changes locally imprinted on the passing electron wave. Our study opens new vistas in the study of multiphoton exchanges between electron beams and evanescent optical fields with unexplored effects related to the transversal component of the electron wave function.
The plasmon damping has been investigated using resonant microwave absorption of two-dimensional electrons in disks with different diameters. We have found an unexpected drastic reduction of the plasmon damping in the regime of strong retardation. This finding implies large delocalization of retarded plasmon field outside the plane of the two-dimensional electron system. A universal relation between the damping of plasmon polariton waves and retardation parameter is reported.
Launching of surface plasmons by swift electrons has long been utilized in electron-energy-loss spectroscopy (EELS) to investigate plasmonic properties of ultrathin, or two-dimensional (2D), electron systems. However, its spatio-temporal process has never been revealed. This is because the impact of an electron will generate not only plasmons, but also photons, whose emission cannot be achieved at a single space-time point, as fundamentally determined from the uncertainty principle. Here, we propose that such a space-time limitation also applies to surface plasmon generation in EELS experiment. On the platform of graphene, we demonstrate within the framework of classical electrodynamics that the launching of 2D plasmons by an electrons impact is delayed after a hydrodynamic splashing-like process, which occurs during the plasmonic formation time when the electron traverses the formation zone. Considering this newly revealed process, we show that previous estimates on the yields of graphene plasmons in EELS have been overestimated.
We study the electromagnetic response and surface electromagnetic modes in a generic gapped Dirac material under pumping with circularly polarized light. The valley imbalance due to pumping leads to a net Berry curvature, giving rise to a finite transverse conductivity. We discuss the appearance of nonreciprocal chiral edge modes, their hybridization and waveguiding in a nanoribbon geometry, and giant polarization rotation in nanoribbon arrays.
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