Midinfrared Ultrastrong LightâMatter Coupling for THz Thermal

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Mid-Infrared ultra-strong light-matter coupling for THz thermal emission Benjamin Askenazi, Angela Vasanelli, Yanko Todorov, Emilie Sakat, JeanJacques Greffet, Grégoire Beaudoin, Isabelle Sagnes, and Carlo Sirtori ACS Photonics, Just Accepted Manuscript • DOI: 10.1021/acsphotonics.7b00838 • Publication Date (Web): 22 Sep 2017 Downloaded from http://pubs.acs.org on September 24, 2017

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Mid-Infrared ultra-strong light-matter coupling for THz thermal emission Benjamin Askenazi1, Angela Vasanelli1, Yanko Todorov1, Emilie Sakat2, Jean-Jacques Greffet2, Grégoire Beaudoin3, Isabelle Sagnes3 and Carlo Sirtori1 1

Univ. Paris Diderot, Sorbonne Paris Cité, Laboratoire Matériaux et Phénomènes Quantiques, UMR7162, F-75013 Paris, France 2

Laboratoire Charles Fabry, Institut d'Optique Graduate School, CNRS, Université ParisSaclay, 91127 Palaiseau, France 3

Centre de Nanosciences et de Nanotechnologies, CNRS, Univ. Paris-Sud, UMR9001, Université Paris-Saclay, C2N Marcoussis, F-91460

*Corresponding author: [email protected]

Abstract In condensed matter, THz optical resonances (1 – 5 THz) are very sensitive to thermally activated phenomena that can either equate the populations between the levels or irremediably broaden the transition to a point where it disappears. It is therefore very difficult to exploit THz electronic transitions for thermal emission. To bypass this problem, we have used a transition in the mid-infrared, (10 – 50 THz) ultra-strongly coupled to a resonant mode of a highly subwavelength microcavity. The coupling strength in our system reaches 90% of the energy of the matter resonance, and becomes so high that the lower-polariton state lies in the THz region. This mixed light-matter resonance is therefore issued from an optical transition that is much less sensitive to thermal effects, as we have experimentally demonstrated. Our

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system has been optimized by tailoring the cavity thickness and engineering the matter resonance, which arises from a set of heavily doped quantum wells, in order to increase the THz emissivity. By injecting a lateral current in the quantum wells that raises the electronic temperature, we have observed THz emission up to room temperature.

Keywords: THz, ultra-strong light-matter coupling, incandescence, plasmons, MIM resonators


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Ultra-strong light-matter coupling is a regime of quantum electrodynamics that occurs when the light-matter coupling energy ER is of the same order of magnitude as the matter excitation energy1. Similarly to the strong coupling regime, the eigenstates of the system, the polaritons, are mixed states involving a matter and a photonic part2. In the ultra-strong configuration, however, a wide gap opens up in the polaritonic dispersion3 that compresses the lower polariton branch at very low energy, as it is illustrated in Fig. 1a. The ultra-strong coupling allows us therefore to take advantage of a robust matter resonance in the midinfrared spectrum (100 – 200 meV) to generate a polaritonic mode in the THz region (15 – 25 meV), almost one order of magnitude lower. Note that, in the limit of ER equal to the matter excitation, the lower polariton (LP) vanishes and only the upper polariton (UP) survives4. In this work we have exploited this property to demonstrate a quasi-monochromatic THz incandescent source. Our device does not need to be cooled, as opposed to usual THz electroluminescent sources. The resonance at THz frequencies arises from the ultra-strong coupling of a mid-infrared collective excitation4, in a doped semiconductor layer, known as Berreman mode5, with a plasmonic microcavity mode. The incandescent emission is excited by a current flowing in the semiconductor layer and then extracted from the top surface by a metallic grating. Our device architecture presents three main advantages with respect to THz incandescent devices existing in the literature. First of all, only the absorbing medium is heated6,7, thus allowing a faster frequency modulation of the incandescence compared to systems in which the entire structure is heated8,9,10. The second advantage resides in the fact that our device is based on a robust mid-infrared collective mode, instead of a single particle THz excitation11. This has an important consequence on the robustness in temperature of the material resonance. Indeed a collective mode has a harmonic oscillator spectrum, which cannot be saturated when increasing the temperature, as opposed to the case of a two level system. Furthermore, the collective mode is issued from the excitation of an electron gas with


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Fermi energy much larger than kBT: the electronic distribution is thus almost unaffected by the temperature. The third advantage of our device is the fact that the photonic structure operates as a microcavity and also as an antenna, thus insuring a good coupling of the polariton modes with the free space 12,13.

Figure 1: (a) Polaritonic dispersion issued from the ultra-strong coupling of a mid-infrared electronic excitation (red dashed line) and a microcavity mode. (b) Sketch of the device. The inset presents a scanning electron microscope image of the microcavities. (c) Scanning electron microscope image of the device. A sketch of our device is illustrated in Fig. 1b. In Fig. 1c, one can see a scanning electron microscope (SEM) picture of real device, composed of an array of metal-dielectricmetal microcavities (a SEM picture is shown in the inset) in which highly doped GaInAs


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semiconductor layers are embedded. The principle of operation of these cavities and the experimental and theoretical characterization of their modes are presented in ref. [14]. The width s of the stripes determines the energy of the cavity mode, while the period p=s+o (where o is the separation between the stripes) and the cavity thickness w fix the coupling to free space radiation14,15. These cavities have been widely used to achieve the strong coupling regime with collective electronic excitations3,4,16. In this work, as explained further, we have simultaneously optimized the photonic resonators and the sequence of doped layers in order to achieve the ultra-strong coupling regime. Furthermore, the semiconductor layer between the gold stripes has been etched in order to improve the confinement of the THz cavity mode. The ultra-strong coupling regime is achieved by tuning the TM0 mode of the resonators close to the energy of the collective excitation of the electron gas in the doped semiconductor layer4,5. In our device we have engineered the intersubband polariton dispersion, shown in Fig. 1a, with the upper branch in the mid-infrared and the lower branch in the THz range, respectively above and below the phonon Reststrahlen band. The polariton states are thermally excited by an increase of the electronic temperature due to a current applied in the plane of the doped semiconductor layers11, while the bottom of the substrate is kept at heat sink temperature TS. The resulting temperature field in the typical conditions of operation of the device is depicted in Fig. 2. The increase of electronic temperature gives rise to THz incandescent emission from the lower polariton branch, which is measured from the surface of the device. To model the temperature, we have introduced a continuous and uniform power source in the active region. An effective thermal conductivity in the stripes accounts for the thermal boundary resistance and for the non-equilibrium between electrons and phonons. This yields a parabolic temperature profile in the stripes and a linear profile in the substrate. This simple model agrees quantitatively with a finite element simulation. Nevertheless, as it will be discussed in the following, the value of the temperature


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increase in the structure is overestimated in this simplified modelling of heat propagation in the device.

Figure 2 : Temperature field in the device when the substrate is at 300K and the electrical power injected in the mesa containing the microcavities is 1.6 W. The size of a mesa is 700 µm x 300 µm, and it contains ~34 stripes of 300µm length and 1-8µm width. A major difficulty that we encountered in the design of our structure is the choice of its thickness in order to maximize the emissivity, i.e. its coupling with the free space. As a matter of fact, the huge energy separation between the two polaritons makes it impossible to have them both equally coupled to free space. According to Kirchhoff’s law, the emissivity is equal to the absorptivity and, since our structure has no transmission, this absorptivity is 1-R, with R the reflectivity. In order to optimize the coupling of the THz mode, we chose the energy of the LP mode at 20 meV and we simulate the reflectivity of the structure by using a finite element commercial software. The results of our simulation are presented in Fig. 3a, where we plot the contrast of the lower polariton mode, defined as 1-Rmin (with Rmin the minimum value of the reflectivity), as a function of the thickness of the cavity w. In this


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simulation the thickness of the AlInAs barriers on both sides of the doped GaInAs layer is adjusted such that the ratio between the thickness of the GaInAs layer and w is constant, thus ensuring that the overlap between the cavity mode and the matter excitation is approximately constant. Figure 3a shows that the LP contrast (and consequently the LP contribution to the emissivity) monotonously increases with the thickness w. However, the shape of the spectra also changes quite substantially as reported in Fig. 3b, where simulated reflectivity spectra for different cavity thicknesses and for fixed values of p = 4µm (s=2µm and o=2µm) are illustrated. Indeed, only for w = 0.25µm and w = 0.5µm, two reflectivity minima, corresponding to the upper and lower polariton, are visible. In both cases the upper polariton (at 140 meV) has a much greater contrast than the lower polariton (at 27 meV). This can be readily understood in terms of impedance mismatch of the cavity modes with the free space, as the wavelength of the LP is 5 times longer than that of the UP. In other words, only the UP mode is close to the critical coupling condition. When increasing the thickness, several modes become visible at high energies. They are due to the coupling between the collective excitation with high order cavity modes in the vertical direction. In order to have a high contrast while avoiding the presence of higher order polariton modes in the spectral region of interest, we have set the cavity thickness to 3µm. Note that with this thickness the upper polariton mode cannot be clearly observed. The optical characterization of the devices will thus focus exclusively on the THz region. To further enhance the light-matter interaction we have also optimized the overlap between the doped layers and the electric field by filling the cavity with an alternating sequence of doped GaInAs/undoped AlInAs layers. Our final device is thus composed of 18 identical periods of 148nm highly doped (5 x 1018 cm-3) GaInAs layers, with a collective mode at Eexc= 99meV, separated by 20nm AlInAs layers.


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Figure 3: (a) Simulated contrast of the LP as a function of the thickness (w) of the cavity, while keeping constant the overlap between the doped layer and the cavity mode. (b) Simulated reflectivity spectra for different cavity thicknesses and for fixed values of p = 4µm (s=2µm and o=2µm). Reflectivity measurements at almost normal incidence (10°) and room temperature for different sizes s of the stripes have been performed on the sample. The incident light from a Globar lamp is focused on the surface of the sample through a mask, so as to illuminate the array of stripes. The reflected beam is focused on a helium cooled silicon bolometer through a parabolic mirror. Figure 4a presents the measured reflectivity spectra (solid line) offset for clarity, for different values of the stripe width s. In order to understand the origin of the different minima, whose energy position varies with s, we have simulated the reflectivity by using a commercial finite element solver. We have included in the simulations (dotted lines in Fig. 4a) the dispersion of the doped layers and of the GaInAs and AlInAs phonons following


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ref. [4]. The energy positions of the reflectivity minima are well reproduced without any adjustable parameter. Nevertheless, the linewidths are broader in the measured spectra. We have verified that the wider broadening can be reproduced by our simulations by taking into account a ~10% inhomogeneity of the dimensions of the stripes (also observed by scanning electron microscope measurements) and non-perfectly vertical sides of the etched stripes (we have measured ~80° inclination).

Figure 4. (a) Reflectivity spectra measured (solid lines) and simulated (dotted lines) at 10° incidence angle for different sizes of the cavities. The red line is a guide for the eyes for the LP branch. (b) Energy position of the reflectivity minima extracted from experiments (bullets) and simulations (solid lines) plotted as a function of the inverse stripe dimension. The stars indicate the energy position of the maxima of the emission spectra. The green dashed line is


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the calculated dispersion without taking into account the phonon modes. The blue region indicate the phonon Reststrahlen band. (c) Effective index extracted from the experimental (bullets) and simulated (red line) reflectivity spectra. The black line is the effective index calculated for a microcavity identical to that used in our experiment, but with undoped GaInAs layers (i.e. without collective electronic excitations). In Fig. 4b we report the energy position of the reflectivity minima (bullets) as a function of 1/s, compared with the calculated polariton dispersion (lines). The lower polariton branch is indicated in red, while the blue lines and symbols indicate phonon – polariton modes, issued from the coupling between the fundamental cavity mode, the collective excitation and LO- and TO- phonon modes in both GaInAs and AlInAs17,18. The measured dispersion is very well reproduced by our simulations. The green dashed line presents the dispersion of the lower polariton branch calculated when neglecting the coupling with optical phonons. This dispersion presents a horizontal asymptote at 38meV, thus within the phonon Reststrahlen band. The coupling with the optical phonons thus strongly affects the energy position of the lower polariton mode for s < 2.5µm. For small dimensions of the stripes the polariton has thus not only a photonic and an electronic component, but also a phononic one. Note that it is not possible to extract the Rabi energy directly from the measurements, as the upper polariton branch dispersion cannot be observed due to the higher order vertical modes. However, the coupling energy can be extracted asymptotically from the fit of the lower polariton dispersion (without considering the coupling with phonons, green dashed line) by using the following equation3,4,19:

1 2 2 ELP =  Eexc + Ec2 − 2

(E

2 c

2 2 − Eexc ) + 4ER2 Ec2 


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and by using our electromagnetic simulations for the cavity mode energy Ec. We obtain a vacuum Rabi splitting ER=90 meV, corresponding to a ratio ER/Eexc = 91%. This is the highest reported value at room temperature for this figure of merit of the ultra-strong coupling regime4. Figure 4c presents the effective index of the lower polariton mode14, obtained as

( ) =

ℏ

=

, from the experimental data (red points) and from the simulations

(red line). It is compared with the effective index of the fundamental mode of an equivalent array of metallic stripes, embedding undoped GaInAs (black line). The low-energy value of the effective index, neff, before the resonance with the phonon bands, gives us a measure of the photon confinement in the cavity. The effective index in the ultra-strongly coupled structure (neff = 9) is more than twice that of the bare cavity (neff = 4). The weight of the matter excitation, therefore, profoundly modifies the light confinement within the cavity, even if the original optical resonance in the mid infrared is spectrally very far apart. Electromagnetic energy is thus confined within cavities with much smaller physical dimensions than wavelength. The sample has been processed to perform incandescence spectra under the injection of an in-plane current in the doped GaInAs layers11,20. The processing is quite challenging, as we have to avoid short-circuit between the electrical contacts on the quantum wells and the bottom gold mirror. A 140 nm thick SiO2 film is deposited by PECVD on the epitaxial layer for electrical isolation before metallization and wafer bonding onto a hosting substrate. After removal of the original substrate, 300µm x 300µm regions containing arrays of stripes are defined using optical lithography, Ti/Au metallization, and lift-off techniques. A Si3N4 layer, 1.55µm thick, was used as a mask in order to etch the semiconductor layer between the metallic cavities, until the SiO2 bottom layer. Last fabrication step is the realisation of the


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electrical contacts for in-plane current injection. For this we have realized a mesa, containing the stripe arrays (with o=6µm) and two 200µm x 300µm regions recovered of gold for wire bonding. In order to contact the 18 GaInAs doped layers, we have evaporated Ni/Ge/Au layers (12nm, 72nm, 144nm) on the side of the sample with 45° angle, annealed at 250°. SEM images of the device can be seen in Fig. 1c. The spectra have been measured from the surface of the sample, at normal direction, by using lock-in techniques, under application of an in-plane current, modulated at 87Hz with 50% duty cycle. Thermal emission from the sample is collected by a parabolic mirror, and then measured by a Fourier Transform Infrared spectrometer operated under vacuum and connected to a helium cooled silicon bolometer. Figure 5a presents the spectra measured at room temperature (for light polarized perpendicularly to the stripes) for four different dimensions of the stripes. The emission peak appears on a thermal background with a dependence on 1/s as measured in reflectivity (see stars in figure 4b) and indicate that the emission is from the lower polariton mode. Note that thanks to the high effective index induced by the ultra-strong coupling, 60µm radiation is emitted by a cavity with less than 3µm width. Figure 5b shows three normalized emission spectra, after subtracting the thermal background, measured from a device of dimension s=2.84µm at heat sink temperature TS=4K, TS=77K and TS=300K. From this figure, it can be clearly seen that the temperature has no significant effects on the shape of the spectra. However, the temperature has an impact on the incandescent emission intensity. The temperature dependence of the power emitted by the lower polariton has been studied by extracting the Lorentzian contribution of the polariton emission from the thermal background and from the phonon resonances in the spectra. Figure 5c presents the temperature dependence of the total power emitted by the lower polariton, estimated after an accurate calibration of our experimental set-up, on a sample with s=2.84


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µm, for a fixed average electrical power of 1.6W. The THz emitted power linearly increases with the temperature, and it attains 4.5 nW at room temperature. Note that this monotonous increase of the emitted power with temperature is unusual for THz intersubband devices, as the incandescent emission typically decreases when increasing the temperature, due to the thermal distribution of electrons in the excited subbands11,20. This temperature behavior of our device can be ascribed to the thermal stability of the collective mode in the mid-infrared, generating THz emission through ultra-strong light-matter coupling “down conversion”.

Figure 5. (a) Emission spectra measured at room temperature from the surface of the device for different widths (s) of the stripes. (b) Emission spectra at three different heat sink temperatures for s=2.84 µm after subtracting the thermal background. The spectra have been


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normalized to the maximum. (c) Power emitted by the lower polariton as a function of the temperature, for a sample with s=2.84 µm. All the data in the panels have been taken for an injected electrical power of 1.6W. We applied a theoretical model to simulate the experimental dependence of the emitted power with temperature. This requires a generalized Kirchhoff law7 to account for the spatial dependence of the temperature. We use the effective thermal resistance as a fitting parameter. We found that the experimental results can be reproduced by considering an effective thermal resistance ~6 x 10-7 m2K/W, which is two orders of magnitude higher than values of thermal boundary resistance found in the literature. We are currently investigating the origin of this anomaly. We find a maximum temperature in the mesa on the order of 1000 K when the substrate is at 300K and an emitted power of 4.2 nW in agreement with the measured power. In conclusion, we fabricated a semiconductor THz incandescent emitter by quantum engineering a mid-infrared collective resonance. This has been realized by operating the device in the ultra-strong light-matter coupling regime with a record value of the relative Rabi energy. As only the electron gas region is heated, by the application of an in-plane current, the device can be modulated very fast21,22. Arrays of different dimensions could be realized on the same device23, in order to obtain quasi-monochromatic emission in a wide frequency range in the THz region following the polaritonic dispersion. Acknowledgments. We acknowledge financial support from ERC (grant ADEQUATE), Renatech Network and Agence Nationale de la Recherche (grant ANR-14-CE26-0023-01).We thank Maria Amanti and Stéphane Suffit for fruitful discussions on the device fabrication.


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REFERENCES (1) Ciuti, C.; Bastard, G.; Carusotto, I. Quantum vacuum properties of the intersubband cavity polariton field. Phys. Rev. B 2005, 72, 115303. (2) Weisbuch, C.; Nishioka, M.; Ishikawa A.; Arakawa, Y. Observation of the coupled exciton-photon mode splitting in a semiconductor quantum microcavity. Phys. Rev. Lett. 1992 69, 3314. (3) Todorov, Y.; Andrews, A. M.; Colombelli, R.; De Liberato, S.; Ciuti, C.; Klang, P.; Strasser G.; Sirtori, C. Ultrastrong Light-Matter Coupling Regime with Polariton Dots. Phys. Rev. Lett. 2010 105, 196402. (4) Askenazi, B.; Vasanelli, A.; Delteil, A.; Todorov, Y.; Andreani, L. C.; Beaudoin, G.; Sagnes, I.; Sirtori, C. Ultra-strong light–matter coupling for designer Reststrahlen band. New Journal of Physics 2014 16, 043029. (5) Harbecke, B.; Heinz B.; Grosse, P.; Optical properties of thin films and the Berreman effect. Appl. Phys. A 1985 38, 263. (6) Laurent, T.; Todorov, Y.; Vasanelli, A.; Delteil, A.; Sirtori, C. ; Beaudoin, G.; Sagnes, I. Superradiant Emission from a Collective Excitation in a Semiconductor. Phys. Rev. Lett. 2015 115, 187402. (7) Greffet, J.-J.; Bouchon, P.; Brucoli, G.; Sakat, E.; Marquier, F. Generalized Kirchhoff law. 2016 arXiv :1601.00312v1 (8) Diem, M.; Koschny, T.; Soukoulis, C. M. Wide-angle perfect absorber/thermal emitter in the terahertz regime. Phys. Rev. B 2009 79, 033101. (9) Alves, F.; Kearney, B.; Grbovic, D.; Karunasiri, G. Narrowband terahertz emitters using metamaterial films. Optics Express 2012 20, 21025. (10) Streyer, W.; Feng, K.; Zhong, Y.; Hoffman, A. J.; Wasserman, D. Selective absorbers and thermal emitters for far-infrared wavelengths. Appl. Phys. Lett. 2015 107, 081105.


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(11) Geiser, M.; Scalari, G.; Castellano, F. ; Beck, M.; Faist, J. Room temperature terahertz polariton emitter. Appl. Phys. Lett. 2012 101, 141118. (12) Madéo, J.; Todorov, Y.; Gilman, A.; Frucci, G.; Li, L. H.; Davies, A. G.; Linfield, E. H.; Sirtori, C.; Dani, K. M. Patch antenna microcavity terahertz sources with enhanced emission. Appl. Phys. Lett. 2016 109, 141103. (13) Palaferri, D.; Todorov, Y.; Mottaghizadeh, A.; Frucci, G.; Biasiol G.; Sirtori, C. Ultrasubwavelength resonators for high temperature high performance quantum detectors. New J. Phys. 2016 18, 113016. (14) Todorov, Y.; Tosetto, L.; Teissier, J.; Andrews, A. M.; Klang, P.; Colombelli, R.; Sagnes, I.; Strasser G.; Sirtori, C. Optical properties of metal-dielectric-metal microcavities in the THz frequency range. Optics Express 2010 18, 13886. (15) Jouy, P.; Todorov, Y.; Vasanelli, A.; Colombelli, R.; Sagnes, I.; Sirtori, C. Coupling of a surface plasmon with localized subwavelength microcavity modes. Appl. Phys. Lett. 2011 98, 021105. (16) Vasanelli, A.; Todorov, Y.; Sirtori, C. Ultra-strong light–matter coupling and superradiance using dense electron gases, C. R. Physique 2016 17, 861–873. (17) Compagnone, F.; Di Carlo A.; Lugli, P. Electron – optical phonon interaction in the In1xGaxAs/In1-y/AlyAs

superlattice. Phys. Rev. B 2002 65, 125314.

(18) Debernardi, A. Phonon linewidth in III-V semiconductors from density-functional perturbation theory. Phys. Rev. B 1998 57, 12847. (19) Delteil, A.; Vasanelli, A.; Todorov, Y.; Feuillet-Palma, C.; Renaudat St-Jean, M.; Beaudoin, G.; Sagnes I.; Sirtori, C. Charge-Induced Coherence between Intersubband Plasmons in a Quantum Structure. Phys. Rev. Lett. 2012 109, 246808.


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(20) Ulrich, J.; Zobl, R.; Unterrainer, K.; Strasser, G.; Gornik, E.; Maranowski, K.; Gossard, A. Temperature dependence of far-infrared electroluminescence in parabolic quantum wells. Appl. Phys. Lett. 1999 74, 3158. (21) Huppert, S.; Vasanelli, A.; Laurent, T.; Todorov, Y.; Pegolotti, G.; Beaudoin,G.; Sagnes, I.; Sirtori, C. Radiatively Broadened Incandescent Sources, ACS Photonics 2015 2, 1663. (22) Inoue, T.; De Zoysa, M.; Asano, T.; Noda, S. Realization of dynamic thermal emission control, Nature Materials 2014 13, 928. (23) Bouchon, P.; Koechlin, C.; Pardo, F.; Haïdar, R.; Pelouard J.-L. Wideband omnidirectional infrared absorber with a patchwork of plasmonic nanoantennas, Optics Letters 2012 37, 1038


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Manuscript title: Mid-Infrared ultra-strong light-matter coupling for THz thermal emission Authors: Benjamin Askenazi, Angela Vasanelli, Yanko Todorov, Emilie Sakat, Jean-Jacques Greffet, Grégoire Beaudoin, Isabelle Sagnes and Carlo Sirtori Graphic description: We realize a device emitting thermal radiation in the THz frequency range. Our device is based on an array of metal- dielectric – metal microcavities, containing highly doped semiconductor layers displaying a collective mode in the mid-infrared. The ultra-strong coupling between the cavity mode and the collective excitations gives rise to a THz mode, which is thermally excited by injecting a current in the semiconductor layer. THz radiation is emitted from the surface of the device and it increases when increasing the operation temperature of the device.


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Midinfrared Ultrastrong LightâMatter Coupling for THz Thermal

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