An engineered planar plasmonic reflector for polaritonic mode confinement

It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, coupling to propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling strength. In this work, we show how plasmonic subwavelength reflectors can be used to create an artificial energy stopband in the plasmon dispersion, confining them and enabling the recovery of the polaritonic resonances. Using this approach we demonstrate a normalized light-matter coupling ratio of {\Omega}/{\omega} = 0.35 employing a single quantum well with a gap size of {\lambda}/2400 in vacuum.Comment: 13 pages, 3 figure

Landau polaritons in highly non-parabolic 2D gases in the ultra-strong coupling regime

We probe ultra-strong light matter coupling between metallic terahertz metasurfaces and Landau-level transitions in high mobility 2D electron and hole gases. We utilize heavy-hole cyclotron resonances in strained Ge and electron cyclotron resonances in InSb quantum wells, both within highly non-parabolic bands, and compare our results to well known parabolic AlGaAs/GaAs quantum well (QW) systems. Tuning the coupling strength of the system by two methods, lithographically and by optical pumping, we observe a novel behavior clearly deviating from the standard Hopfield model previously verified in cavity quantum electrodynamics: an opening of a lower polaritonic gap

Polaritonic nonlocality in light-matter interaction

Subwavelength electromagnetic field localization has been central to photonic research in the last decade, allowing us to enhance sensing capabilities as well as increase the coupling between photons and material excitations. The strong and ultrastrong light–matter coupling regime in the terahertz range using split-ring resonators coupled to magnetoplasmons has been widely investigated, achieving successive world records for the largest light–matter coupling ever achieved. Ever shrinking resonators have allowed us to approach the regime of few-electron strong coupling, in which single-dipole properties can be modified by the vacuum field. Here, we demonstrate, theoretically and experimentally, the existence of a limit to the possibility of arbitrarily increasing electromagnetic confinement in polaritonic systems. Strongly subwavelength fields can excite a continuum of high-momenta propagative magnetoplasmons. This leads to peculiar nonlocal polaritonic effects, as certain polaritonic features disappear and the system enters the regime of discrete-to-continuum strong coupling.ISSN:1749-4885ISSN:1749-489

Polaritonic nonlocality in light-matter interaction

Sub-wavelength electromagnetic field localization has been central in photonic research in the last decade, allowing to enhance sensing capabilities as well as increasing the coupling between photons and material excitations. The strong and ultrastrong light-matter coupling regime in the THz range with split-ring resonators coupled to magnetoplasmons has been widely investigated, achieving successive world-records for the largest light-matter coupling ever achieved Ever shrinking resonators have allowed to approach the regime of few electrons strong coupling, in which single-dipole properties can be modified by the vacuum field. Here we demonstrate, theoretically and experimentally, the existence of a limit to the possibility of arbitrarily increasing electromagnetic confinement in polaritonic systems. Strongly sub-wavelength fields can excite a continuum of high-momenta propagative magnetoplasmons. This leads to peculiar nonlocal polaritonic effects, as certain polaritonic features disappear and the system enters in the regime of discrete-to-continuum strong coupling<br/

THz Ultrastrong Coupling in an Engineered Fabry-Perot Cavity

We report a monolithic THz planar Fabry-Perot cavity fabricated with wafer bonding and provided with metallic mirrors with subwavelength apertures. We demonstrate its coupling to the cyclotron resonance of a high-mobility, two-dimensional electron gas. Q factors up to 89 are observed for the first mode at similar or equal to 300 GHz, with cooperativity C = 56.4 and a normalized coupling ratio Omega/omega in the first mode of up to 17.5% and the third mode of up to 6.4%.ISSN:2330-402

Engineered planar plasmonic reflector for polaritonic mode confinement [Invited]

It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling strength. In this work, we show how plasmonic reflectors can be used to create an artificial energy stopband in the plasmon dispersion, confining them and enabling the recovery of the polaritonic resonances. Using this approach we demonstrate a normalized light-matter coupling ratio of ΩωR0 = 0.36 employing a single doped quantum well with a resonator’s gap size of 250 nm equivalent to λ/3000 in vacuum, a geometry in which the polaritonic resonances would not be observable in the absence of the plasmonic reflectors.ISSN:2159-393

An engineered planar plasmonic reflector for polaritonic mode confinement

It was recently demonstrated that, in deep subwavelength gap resonators coupled to two-dimensional electron gases, propagating plasmons can lead to energy leakage and prevent the formation of polaritonic resonances. This process, akin to Landau damping, limits the achievable field confinement and thus the value of light-matter coupling strength. In this work, we show how plasmonic reflectors can be used to create an artificial energy stopband in the plasmon dispersion, confining them and enabling the recovery of the polaritonic resonances. Using this approach we demonstrate a normalized light-matter coupling ratio of ΩR/ω0 = 0.36 employing a single doped quantum well with a resonator's gap size of 250 nm equivalent to λ/3000 in vacuum, a geometry in which the polaritonic resonances would not be observable in the absence of the plasmonic reflectors