Polaritons in van der Waals materials

Abstract

Polaritons in van der Waals (vdW) materials. Polaritons-a hybrid of light-matter oscillations-can originate in different physical phenomena: conduction electrons in graphene and topological insulators (surface plasmon polaritons), infrared-active phonons in boron nitride (phonon polaritons), excitons in dichalcogenide materials (exciton polaritons), superfluidity in FeSe-and Cu-based superconductors with high critical temperature T c (Cooper-pair polaritons), and magnetic resonances (magnon polaritons). The family of vdW materials supports all of these polaritons. The matter oscillation component results in negative permittivity (e B < 0) of the polaritonic material, giving rise to optical-field confinement at the interface with a positive-permittivity (e A > 0) environment. vdW polaritons exhibit strong confinement, as defined by the ratio of incident light wavelength l 0 to polariton wavelength l p .

Towards properties on demand in quantum materials

“…A familiar example of photon dressing (pictured, panel a) occurs as the result of light hybridization with dipole-active excitations in solids and is best revealed in the energy-momentum (E-k) dispersion. Polaritonic effects are especially rich in van der Waals atomic layers and crystals that support a full suite of these hybrid quasiparticles stemming from coupling to plasmons, phonons, excitions and magnons 57 . A high degree of confinement of polaritonic modes combined with relatively weak losses allows one to control and manipulate long-wavelength electromagnetic radiation at nanometre length scales.…”

“…These quasiparticles (Box 1, panel a) are hybrids of light and matter involving collective oscillations of charges in materials 25,57 . The most thoroughly investigated and utilized of these are surface plasmon-polaritons supported by electrons in conducting media and light.…”

Ultrafast Multiphoton Thermionic Photoemission from Graphite

“…As electricity emerged from the laboratory, the first optoelectronic devices, incandescent light bulbs, converted electricity to light by Ohmic heating of carriers within graphitized bamboo fibers. More recently, graphene has been identified as a material with remarkable optical and electronic properties for numerous applications [9][10][11] and has sparked interest in novel physical properties of two-dimensional (2D) materials [12,13]. As a semimetal, under linear optical excitation, graphene is nonemissive, but under nonlinear optical or electrical stimulation, it can emit both intense incandescence characterized by blackbody radiation temperatures in excess of 3000 K and broadband coherent radiation [14][15][16][17].…”

Far Infrared Synchrotron Near-Field Nanoimaging and Nanospectroscopy

“…4, with FIR SINS we observe a significant enhancement of the low energy SiO 2 phonon mode and direct absorption of graphene plasmons, suggesting a very strong plasmon-phonon coupling that is highly tunable with gating. This also opens up new opportunities for studying a wide range of corresponding modes in 2D and Dirac materials, including transition metal dichalcogenides, black phosphorous, and topological insulators, which typically host plasmons at FIR energies [13]. Further, large intrinsic anisotropies in these and other polar dielectric crystals can be explored for use as natural hyperbolic materials for unique nano-photonics applications in the FIR, without the need for artificial metamaterials with high losses [41], all with nanoscale spatial resolution.…”

“…It provides for nano-imaging and -spectroscopy down to few nanometer length scales, gaining insight into molecular orientation [5] and coupling [6], catalytic activity [7], heterogeneity in electron and lattice dynamics [8,9], and plasmonic and polaritonic effects in quantum matter [10][11][12][13] with recent extension to the low temperature [9,14] and ultrafast regimes [15][16][17][18]. Despite these significant developments, s-SNOM has largely been limited to a narrow range of the electromagnetic spectrum of the near-to mid-IR at high frequencies, and the RF [19] and low THz [20] regime at low frequencies.…”