Gate-tunable negative refraction of mid-infrared polaritons

Abstract

Negative refraction provides a platform to manipulate mid-infrared and terahertz radiation for molecular sensing and thermal emission applications. However, its implementation based on metamaterials and plasmonic media presents challenges with optical losses, limited spatial confinement, and lack of active tunability in this spectral range. We demonstrate gate-tunable negative refraction at mid-infrared frequencies using hybrid topological polaritons in van der Waals heterostructures. Specifically, we visualize wide-angle negatively refracted polaritons in α-MoO 3 films partially decorated with graphene, undergoing reversible planar nanoscale focusing. Our atomically thick heterostructures weaken scattering losses at the interface while enabling an actively tunable transition of normal to negative refraction through electrical gating. We propose polaritonic negative refraction as a promising platform for infrared applications such as electrically tunable super-resolution imaging, nanoscale thermal manipulation, enhanced molecular sensing, and on-chip optical circuitry.

High-efficiency in situ amplitude and phase control of infrared light using topological polaritons

“…The first one is using a metal gate to apply the electric doping, but it requires quite a high voltage to reach 0.3 eV, which is barely workable. Another one is using NO 2 gas 3 or a RuCl 3 layer 4,43 to pre-dope the graphene to 0.3 eV and then using local metal gates to tune the E F of the graphene in the right region, and in this way, a doping range of 0−0.7 eV can be achieved. By electrostatic simulation, we can obtain the spatial profile of E F in the gap region for the two doping methods, as shown in Fig.…”

“…Moreover, the in-plane anisotropic structure of the α-MoO 3 leading to the in-plane hyperbolic polaritons provides another degree of freedom for surface wave manipulation. Based on α-MoO 3 , many novel phenomena of surface optics have been experimentally investigated, including negative reflection, 35 negative refraction 3,4 and topological transitions (TTs). 3,34 An intuitive and practical direction for the control of polaritons is modulating their amplitudes and phases, which can be considered a scattering problem.…”

“…Polaritons are half-matter half-light modes that originate from the interactions between photons and material excitations. Manipulation of such modes is crucial for many application demands, including subwavelength focusing, 1–6 waveguiding, 7–10 emission enhancement, 11–13 molecular detection and biosensing, 14–19 etc . However, polaritons in traditional bulk materials such as metals and polar dielectrics often suffer from high scattering loss or low electric sensitivity, 20–22 and thus, they are limited in applications.…”

Focusing of Hyperbolic Phonon Polaritons by Bent Metal Nanowires and Their Polarization Dependence

“…The near-field intensity distribution of in-plane hyperbolic focusing affected by the polarization is revealed by modulating the relative angle of the NW to the in-plane polarized light, which is of great significance to guide in-plane modulation efforts. Overall, our work provides new possibilities for deeper investigation of light–matter coupling and guidance modes for low-dimensional nanolens, and polarized wave array-type excitation and focusing provide ideas for molecular sensing, light guidance, energy confinement, ,, etc. It also opens the way for the development of planar photonic applications, such as planar nanoswitches and in-plane heat conduction.…”

Light walking in low-symmetry 2D materials

“…Subsequently, they highlight three types of hyperbolic polaritons (i.e., phonon, plasmon, and exciton polaritons), followed by four manipulation approaches, among which, in our opinion, integrating graphene with low-symmetry 2D materials (or in general, hybridization of 2D materials) will continue to thrive and become the future tendency for research of polaritons [7] . Excitingly, the latest experiment [8] has just indicated the plausibility of gate-tunable plasmon–phonon polaritons in the graphene/α-MoO3 heterostructure. This review also incorporates various applications concerning polaritons to complete the discussion, including polarization engineering [9] (e.g., on-chip wave plates), planar nanophotonics [10] (e.g., nano-focusing, negative refraction), enhancement of spontaneous emission and biosensing, and thermal radiation.…”