title: Optical Nanoimaging of Hyperbolic Surface Polaritons at the Edges of van der Waals Materials.
abstract: Hyperbolic polaritons in van der Waals (vdW) materials recently attract a lot of attention, owing to their strong electromagnetic field confinement, ultraslow group velocities, and long lifetimes. Typically, volume-confined hyperbolic polaritons (HPs) are studied. Here we show the first near-field optical images of hyperbolic surface polaritons (HSPs), which are confined and guided at the edges of thin flakes of a vdW material. To that end, we applied scattering-type scanning near-field optical microscopy (s-SNOM) for launching and real-space nanoimaging of hyperbolic surface phonon polariton modes on a hexagonal boron nitride (h-BN) flake. Our imaging data reveal that the fundamental HSP mode exhibits a stronger field confinement (shorter wavelength), smaller group velocities, and nearly identical lifetimes, as compared to the fundamental HP mode of the same h-BN flake. Our experimental data, corroborated by theory, establish a solid basis for future studies and applications of HPs and HSPs in vdW materials.
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.
authors.forename: P
authors.identifier: 0000-0003-3836-3803
authors.initials: P
authors.lastname: Li
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.
authors.forename: I
authors.initials: I
authors.lastname: Dolado
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.
authors.forename: F J
authors.initials: FJ
authors.lastname: Alfaro-Mozaz
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.|IKERBASQUE , Basque Foundation for Science, 48013 Bilbao, Spain.
authors.forename: A Yu
authors.initials: AY
authors.lastname: Nikitin
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.|IKERBASQUE , Basque Foundation for Science, 48013 Bilbao, Spain.
authors.forename: F
authors.initials: F
authors.lastname: Casanova
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.|IKERBASQUE , Basque Foundation for Science, 48013 Bilbao, Spain.
authors.forename: L E
authors.initials: LE
authors.lastname: Hueso
authors.affiliation: CIC NanoGUNE , 20018, Donostia-San Sebastián, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Vélez
authors.affiliation: IKERBASQUE , Basque Foundation for Science, 48013 Bilbao, Spain.|CIC NanoGUNE and UPV/EHU , 20018, Donostia-San Sebastián, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Hillenbrand
keywords: Dyakonov surface waves; Hyperbolic surface polaritons; h-BN; near-field microscopy; phonon polaritons; s-SNOM; van der Waals materials