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Yanko Todorov

Publications and source records attributed to Yanko Todorov.

At least 19 recordsLinked to original sources
arXiv2026

Polariton-Assisted Inelastic Tunneling through a Quantum Well

We investigate electronic transport through a doped quantum well strongly interacting with a photonic mode confined in a double-metal cavity. Using a nonequilibrium Green's function formalism, we derive compact expressions for the current valid for arbitrary collective light--matter coupling strengths exceeding the relevant loss rates. We show that cavity polaritons leave observable transport signatures when the carrier injection rate is smaller than the cavity-induced electronic broadening. In this regime, the current--voltage characteristics exhibit inelastic sidebands associated with resonant and anti-resonant polariton emission, which are strongly enhanced under resonant illumination. Our results provide a realistic route to detecting cavity-induced modifications of charge transport in semiconductor heterostructures.

cond-mat.mes-hall↗
arXiv2026

Engineering Nanophotonic Modes via the Radiation Continuum

We demonstrate, experimentally and theoretically, a universal mechanism for combining nanophotonic modes relying on radiative-loss-mediated couplings. For the case of two modes this mechanism leads to a BIC-type phenomenon characterized by the emergence of a high-quality factor subradiant mode. This mode is experimentally observed in the mid-infrared range, in arrays of double-metal patch antennas where the radiation loss rates are controlled by the geometry of the system. As the mechanism described here is independent of the specific nature or number of the interacting modes, it can be used to combine physically different resonating structures, without requiring fine symmetry tuning or specific modal configurations, opening new opportunities for resonance-based nanophotonic devices.

physics.optics↗
arXiv2026

Deep Strong light-matter Coupling in 3D Kane Fermions

Deep strong light-matter coupling represents an extreme non-perturbative regime of quantum electrodynamics, in which the interaction strength exceeds the bare frequencies of the uncoupled systems. The ground state features strong quantum correlations between photons and matter excitations, and new cavity-driven phase transitions are expected to occur. Whether a superradiant quantum phase transition, marked by spontaneous dipole ordering and photon condensation, is possible has remained a long-standing and controversial question. Such phenomena have been proposed to arise in exotic electronic systems hosting Dirac and Kane fermions, owing to the formal absence of an $A^2$ term in their low-energy Hamiltonian. Here we exploit the ultralow effective mass of Kane fermions to realise Landau polaritons in a bulk mercury cadmium telluride layer coupled to a Fabry-Perot resonator. Using thermally tunable carrier density, we continuously tune the coupling from the weak to the deep-strong regime, achieving a record normalised coupling ratio exceeding 1.6 above room temperature. The measured polariton spectra are in excellent agreement with a rigorous, gauge-invariant microscopic theory. Despite the nonlinear Landau level structure of relativistic Kane fermions, we show that a diamagnetic $A^2$ term naturally emerges and precludes a superradiant phase transition. These results resolve the long-standing controversy surrounding cavity quantum electrodynamics of relativistic-like matter systems, extend deep-strong-coupling physics to Kane fermions, and open new opportunities for polaritonic semiconductor devices operating in extreme light-matter coupling regimes.

cond-mat.mes-hall↗
arXiv2026

Microscopic quantum description of surface plasmon polaritons: Revealing intrinsic ultrastrong light-matter coupling

We develop a microscopic quantum theory of surface plasmon polaritons valid for arbitrary metal-dielectric geometries. Our framework is based on the Power-Zienau-Woolley representation of quantum electrodynamics, which provides an optimal separation between electronic and photonic degrees of freedom and is therefore particularly well suited for constructing quantum descriptions of polaritonic excitations in strongly dispersive media. Within this formulation, the fundamental electronic oscillator is identified as the bulk plasmon mode, which is nonperturbatively coupled to the radiative continuum of free photon modes. This coupling induces a geometry-dependent renormalization of the bulk plasma frequency, giving rise to confined plasmonic resonances. As specific applications, we recover the localized surface plasmon modes of metallic nanoparticles, including radiative frequency shifts and decay, as well as the exact dispersion relation of propagating surface plasmon polaritons at planar interfaces. Our quantum treatment further reveals that light-matter interactions at metal-dielectric interfaces are inherently in the ultrastrong coupling regime. As a result, in the quasistatic limit, the system exhibits unconventional ground-state quantum fluctuations that can be controlled through the refractive index. These results open new intriguing perspectives in the field of quantum plasmonics.

physics.optics↗
arXiv2025

Three-dimensional Meta-atoms for High Confinement of Mid-IR Radiation

The ability to confine photons into structures with highly sub-wavelength volumes is extremely interesting for many applications such as sensing, nonlinear optics, and strong light-matter interactions. However, their realization is increasingly difficult as the wavelength becomes shorter, due to fabrication challenges and increased metal losses. In this work, we present the first experimental characterization of three-dimensional circuit-like resonators operating in the mid-infrared. Through a combination of simulations, reflectivity measurements, and scanning near-field optical microscopy, we developed an analytical model capable of predicting the electromagnetic response of these structures based on their geometrical parameters. The design we studied offers a high degree of flexibility, enabling precise control over the resonant frequency of the various modes supported by the resonator, as well as independent control over radiative and non-radiative losses. Combined with the extreme field confinement demonstrated, these meta-atoms are highly promising for applications in detectors,

physics.optics↗
arXiv2024

Ultra-sensitive heterodyne detection at room temperature in the atmospheric windows

We report room temperature heterodyne detection of a quantum cascade laser beaten with a local oscillator on a unipolar quantum photodetector in two different atmospheric windows, at 4.8 $\mu$m and 9 $\mu$m. A noise equivalent power of few pW is measured by employing an active stabilization technique in which the local oscillator and the signal are locked in phase. The measured heterodyne noise equivalent power is six orders of magnitude lower than that obtained with direct detection.

physics.optics↗
arXiv2024

Quantum theory for nonlinear optical effects in the ultra-strong light-matter coupling regime

We present a microscopic quantum theory for nonlinear optical phenomena in semiconductor quantum well heterostructures operating in the regime of ultra-strong light matter coupling regime. This work extends the Power-Zienau-Wooley (PZW) formulation of quantum electrodynamics to account for nonlinear interactions based on a fully fermionic approach, without resorting to any bosonization approximation. It provides a unified description of the microcavity and the local field enhancement effects on the nonlinear optical response, thus encompassing the phenomena known as epsilon near zero (ENZ) effect. In particular, our theory describes the impact of the light-matter coupled states on the high frequency generation process, relevant for recent experimental investigations with polaritonic metasurfaces. We unveil the limitations of traditional single-particle approaches and propose novel design principles to optimize nonlinear conversion efficiencies in dense, microcavity-coupled electronic systems. The theoretical framework developed here provides an efficient tool for the development of advanced quantum optical applications in the mid-infrared and terahertz spectral domains. Furthermore, it establishes a foundation for exploring the quantum properties of the ultra-strong light-matter regime through frequency-converted polariton states.

physics.optics↗
arXiv2024

Hybridization of terahertz phonons and magnons in disparate and spatially-separated material specimens

The interaction between light and matter in condensed matter excitations and electromagnetic resonators serves as a rich playground for fundamental research and lies at the core of photonic and quantum technologies. Herein, we present comprehensive experimental and theoretical studies of the photon-mediated hybridization of magnons and phonons in the terahertz (THz) range. We demonstrate the intriguing concept of composite states formed by distinct electric and magnetic quasiparticles strongly coupled to the same optical cavity modes. Specifically, we explore magnons excited in a slab of an antiferromagnetic crystal and phonons excited in a distinct specimen of an insulating material. The crystal slabs form an optical cavity with Fabry-P\'erot oscillations in the THz range. We demonstrate hybridized phonon-magnon polariton modes and their tunability by adjusting the distance between the slabs, showing that hybridization persists even at separations up to several millimeters. The experimental results are interpreted using both classical and quantum electrodynamical models. The quantum description allows us to quantify the degree of hybridization that is linked to a topological behavior of the electric field phasor, in agreement with the classical electrodynamics expectations. Importantly, the presented results refer to temperature conditions and cavities of millimeter size, paving the way for engineering realistic, frequency-tunable THz devices through the hybridization of electric (phononics) and magnetic (spintronics) elementary excitations of matter.

physics.optics↗
arXiv2023

Phonon-mediated dark to bright plasmon conversion

The optical response of a matter excitation embedded in nanophotonic devices is commonly described by the Drude-Lorentz model. Here, we demonstrate that this widely used approach fails in the case where quantum-confined plasmons of a two-dimensional electron gas interact strongly with optical phonons. We propose a new quantum model which contains the semiclassical Drude-Lorentz one for simple electronic potentials, but predicts very different results in symmetry-broken potentials. We unveil a new mechanism for the oscillator strength transfer between bright phonon-polariton and dark plasmon modes, enabling thus new quantum degrees of freedom for designing the optical response of nanostructures.

cond-mat.mes-hall↗
arXiv2020

High temperature metamaterial terahertz quantum detector

We demonstrate a high temperature performance quantum detector of Terahertz (THz) radiation based on three-dimensional metamaterial. The metamaterial unit cell consists of an inductor-capacitor (LC) resonator laterally coupled with antenna elements. The absorbing region, consisting of semiconductor quantum wells is contained in the strongly ultra-subwavelength capacitors of the LC structure. The high radiation loss of the antenna allows strongly increased collection efficiency for the incident THz radiation, while the small effective volume of the LC resonator allows intense light-matter coupling with reduced electrical area. As a result, our detectors operates at much higher temperatures than conventional quantum well detectors demonstrated so far.

physics.optics↗
arXiv2020

Semiconductor quantum plasmonics

We investigate the frontier between classical and quantum plasmonics in highly doped semiconductor layers. The choice of a semiconductor platform instead of metals for our study permits an accurate description of the quantum nature of the electrons constituting the plasmonic response, which is a crucial requirement for quantum plasmonics. Our quantum model allows us to calculate the collective plasmonic resonances from the electronic states determined by an arbitrary one-dimensional potential. Our approach is corroborated with experimental spectra, realized on a single quantum well, in which higher order longitudinal plasmonic modes are present. We demonstrate that their energy depends on the plasma energy, as it is also the case for metals, but also on the size confinement of the constituent electrons. This work opens the way towards the applicability of quantum engineering techniques for semiconductor plasmonics.

cond-mat.mes-hall↗
arXiv2020

Semiconductor quantum plasmons for high frequency thermal emission

Plasmons in heavily doped semiconductor layers are optically active excitations with sharp resonances in the 5-15 um wavelength region set by the doping level and the effective mass. Here we demonstrate that volume plasmons can form in doped layers of widths of hundreds of nanometers, without the need of potential barrier for electronic confinement. Their strong interaction with light makes them perfect absorber and therefore suitable for incandescent emission. Moreover, by injecting microwave current in the doped layer, we can modulate the temperature of the electron gas. We have fabricated devices for high frequency thermal emission and measured incandescent emission up to 50MHz, limited by the cutoff of our detector. The frequency dependent thermal emission is very well reproduced by our theoretical model that let us envision a frequency cutoff in the tens of GHz.

cond-mat.mes-hall↗
arXiv2020

Quasi-static and propagating modes in three-dimensional THz circuits

We provide an analysis of the electromagnetic modes of three-dimensional metamaterial resonators in the THz frequency range. The fundamental resonance of the structures is fully described by an analytical circuit model, which not only reproduces the resonant frequencies but also the coupling of the metamaterial with an incident THz radiation. We also evidence the contribution of the propagation effects, and show how they can be reduced by design. In the optimized design the electric field energy is lumped into ultra-subwavelength ($λ$/100) capacitors, where we insert semiconductor absorber based on the collective electronic excitation in a two dimensional electron gas. The optimized electric field confinement is evidenced by the observation of the ultra-strong light-matter coupling regime, and opens many possible applications for these structures for detectors, modulators and sources of THz radiation.

physics.optics↗
arXiv2020

Long-wavelength infrared photovoltaic heterodyne receivers using patch-antenna quantum cascade detectors

Quantum cascade detectors (QCD) are unipolar infrared devices where the transport of the photo excited carriers takes place through confined electronic states, without an applied bias. In this photovoltaic mode, the detector's noise is not dominated by a dark shot noise process, therefore, performances are less degraded at high temperature with respect to photoconductive detectors. This work describes a 9 um QCD embedded into a patch-antenna metamaterial which operates with state-of-the-art performances. The metamaterial gathers photons on a collection area, Acoll, much bigger than the geometrical area of the detector, improving the signal to noise ratio up to room temperature. The background-limited detectivity at 83 K is 5.5 x 10^10 cm Hz^1/2 W^-1, while at room temperature, the responsivity is 50 mA/W at 0 V bias. Patch antenna QCD is an ideal receiver for a heterodyne detection set-up, where a signal at a frequency 1.4 GHz and T=295 K is reported as first demonstration of uncooled 9um photovoltaic receivers with GHz electrical bandwidth. These findings guide the research towards uncooled IR quantum limited detection.

physics.app-ph↗
arXiv2020

Quantum Theory of Multisubband Plasmon-Phonon Coupling

We present a theoretical description of the coupling between longitudinal optical phonons and collective excitations of a two-dimensional electron gas. By diagonalizing the Hamiltonian of the system, including Coulomb electron-electron and Fröhlich interactions, we observe the formation of multisubband polarons, mixed states partially phonon and partially multisubband plasmon, characterized by a coupling energy which is a significant fraction, up to ~40%, of the phonon energy. We demonstrate that multisubband plasmons and longitudinal optical phonons are in the ultra-strong coupling regime in several III-V and II-VI material systems.

cond-mat.mes-hall↗
arXiv2019

Ultra-Strong Light-Matter Coupling in Deeply Subwavelength THz LC resonators

The ultra-strong light-matter coupling regime has been demonstrated in a novel three-dimensional inductor-capacitor (LC) circuit resonator, embedding a semiconductor two-dimensional electron gas in the capacitive part. The fundamental resonance of the LC circuit interacts with the intersubband plasmon excitation of the electron gas at $ω_c = 3.3$~THz with a normalized coupling strength $2Ω_R/ω_c = 0.27$. Light matter interaction is driven by the quasi-static electric field in the capacitors, and takes place in a highly subwavelength effective volume $V_{\mathrm{eff}} = 10^{-6}λ_0^3$ . This enables the observation of the ultra-strong light-matter coupling with $2.4\times10^3$ electrons only. Notably, our fabrication protocol can be applied to the integration of a semiconductor region into arbitrary nano-engineered three dimensional meta-atoms. This circuit architecture can be considered the building block of metamaterials for ultra-low dark current detectors.

cond-mat.mes-hall↗
arXiv2017

Room temperature 9 $μ$m photodetectors and GHz heterodyne receivers

Room temperature operation is mandatory for any optoelectronics technology which aims to provide low-cost compact systems for widespread applications. In recent years, an important technological effort in this direction has been made in bolometric detection for thermal imaging$^1$, which has delivered relatively high sensitivity and video rate performance ($\sim$ 60 Hz). However, room temperature operation is still beyond reach for semiconductor photodetectors in the 8-12 $μ$m wavelength band$^2$, and all developments for applications such as imaging, environmental remote sensing and laser-based free-space communication$^{3-5}$ have therefore had to be realised at low temperatures. For these devices, high sensitivity and high speed have never been compatible with high temperature operation$^{6, 7}$. Here, we show that a 9 $μ$m quantum well infrared photodetector$^8$, implemented in a metamaterial made of subwavelength metallic resonators$^{9-12}$, has strongly enhanced performances up to room temperature. This occurs because the photonic collection area is increased with respect to the electrical area for each resonator, thus significantly reducing the dark current of the device$^{13}$. Furthermore, we show that our photonic architecture overcomes intrinsic limitations of the material, such as the drop of the electronic drift velocity with temperature$^{14, 15}$, which constrains conventional geometries at cryogenic operation$^6$. Finally, the reduced physical area of the device and its increased responsivity allows us, for the first time, to take advantage of the intrinsic high frequency response of the quantum detector$^7$ at room temperature. By beating two quantum cascade lasers$^{16}$ we have measured the heterodyne signal at high frequencies up to 4 GHz.

physics.app-ph↗