Black phosphorus plasmonics: anisotropic elliptical propagation and nonlocality-induced canalization

Abstract

Abstract:We investigate unusual surface plasmons polariton (SPP) propagation and light-matter interactions in ultrathin black phosphorus (BP) films, a 2D material that exhibits exotic electrical and physical properties due to its extremely anisotropic crystal structure. Recently, it has been speculated that the ultra-confined surface plasmons supported by BP may present various topologies of wave propagation bands, ranging from anisotropic elliptic to hyperbolic, across the mid-and near-infrared regions of the electromagnetic spectrum. By carefully analyzing the natural nonlocal anisotropic optical conductivity of BP, derived using the Kubo formalism and an effective low-energy Hamiltonian, we demonstrate here that the SPP wavenumber cutoff imposed by nonlocality prohibits that they acquire an arbitrary hyperbolic topology, forcing operation in the canalization regime. The resulting nonlocality-induced canalization presents interesting properties, as it is inherently broadband, enables large light-matter interactions in the very near field, and allows extreme device miniaturization. We also determine fundamental bounds to the confinement of BP plasmons, which are significantly weaker than for graphene, thus allowing a larger local density of states. Our results confirm the potential of BP as a promising reconfigurable plasmonic platform, with exciting applications, such as planar hyperlenses, optoelectronic components, imaging, and communication systems.

The Optical Properties and Plasmonics of Anisotropic 2D Materials

“…Therefore, BP films are treated as a model system to host the anisotropic and hyperbolic 2D plasmons . Great theoretical and experimental efforts have been devoted to investigating the plasmons in this natural anisotropic material. Below, we discuss the theoretical studies on the plasmon dynamics of BP films and the experimental progress in detecting BP plasmons, as well as the potential applications of plasmons in anisotropic 2D materials.…”

“…Due to the highly anisotropic in‐plane dynamics, a number of theoretical works were performed to study the plasmons in BP . Low et al studied collective electron excitations in monolayer and multilayer BP within the random phase approximation (RPA) using an effective low‐energy Hamiltonian .…”

“…In the past few years, tremendous attention has been given to graphene plasmons, with a remarkable manifestation of high tunability and low loss . Recently, a number of theoretical efforts have been devoted to studying the plasmonic properties of BP, where anisotropic plasmon dispersions occur due to its band anisotropy . Fascinatingly, the hyperbolic plasmon polaritons, whose iso‐frequency contour is a hyperbola, are predicted to naturally exist in BP films, which originate from the coupling between the intraband and interband optical conductivity .…”

“…Recently, a number of theoretical efforts have been devoted to studying the plasmonic properties of BP, where anisotropic plasmon dispersions occur due to its band anisotropy . Fascinatingly, the hyperbolic plasmon polaritons, whose iso‐frequency contour is a hyperbola, are predicted to naturally exist in BP films, which originate from the coupling between the intraband and interband optical conductivity . This special plasmon topology leads to an anomalously large photonic density of states and directional propagating plasmonic rays, which promises intriguing applications for planar photonics .…”

Tunable plasmon-enhanced birefringence in ribbon array of anisotropic two-dimensional materials

“…Alternately, with the recent isolation of anisotropic 2D materials [22][23][24][25], one can exploit the inherent anisotropy of the crystal lattice to induce the phase anisotropy [26,27]. In homogeneous form, such 2D materials with anisotropic [28,29] and hyperbolic [30,31] polaritonic properties, can be regarded as ideal material platforms to be used as ultra-thin linearly birefringent retarders.In this work, we study light scattering properties in anisotropic 2D materials and show how plasmon excitation in ribbon array (RA) configuration can enable a wide range of control over the amplitude, phase, and polarization state of the scattered light. Through inspection of various scenarios, we found that the mere rotation of the array plane relative to the incident field polarization, or modulation of material Drude weights through control of its carrier density or effective mass, can be adopted to drastically tune the RA optical response.…”