Electrically injected cavity polaritons

We have realised a semiconductor quantum structure that produces electroluminescence while operating in the light-matter strong coupling regime. The mid-infrared light emitting device is composed of a quantum cascade structure embedded in a planar microcavity, based on the GaAs/AlGaAs material system. At zero bias, the structure is characterised using reflectivity measurements which show, up to room temperature, a wide polariton anticrossing between an intersubband transition and the resonant cavity photon mode. Under electrical injection the spectral features of the emitted light change drastically, as electrons are resonantly injected in a reduced part of the polariton branches. Our experiment demonstrates that electrons can be selectively injected into polariton states up to room temperature.Comment: 10 pages, 4 figure

Radiative quantum efficiency in an InAs/AlSb intersubband transition

The quantum efficiency of an electroluminescent intersubband emitter based on InAs/AlSb has been measured as a function of the magnetic field up to 20T. Two series of oscillations periodic in 1/B are observed, corresponding to the elastic and inelastic scattering of electrons of the upper state of the radiative transitions. Experimental results are accurately reproduced by a calculation of the excited state lifetime as a function of the applied magnetic field. The interpretation of these data gives an exact measure of the relative weight of the scattering mechanisms and allows the extraction of material parameters such as the energy dependent electron effective mass and the optical phonon energy.Comment: 4 pages, 5 figure

Bound-to-bound and bound-to-continuum optical transitions in combined quantum dot - superlattice systems

By combining band gap engineering with the self-organized growth of quantum dots, we present a scheme of adjusting the mid-infrared absorption properties to desired energy transitions in quantum dot based photodetectors. Embedding the self organized InAs quantum dots into an AlAs/GaAs superlattice enables us to tune the optical transition energy by changing the superlattice period as well as by changing the growth conditions of the dots. Using a one band envelope function framework we are able, in a fully three dimensional calculation, to predict the photocurrent spectra of these devices as well as their polarization properties. The calculations further predict a strong impact of the dots on the superlattices minibands. The impact of vertical dot alignment or misalignment on the absorption properties of this dot/superlattice structure is investigated. The observed photocurrent spectra of vertically coupled quantum dot stacks show very good agreement with the calculations.In these experiments, vertically coupled quantum dot stacks show the best performance in the desired photodetector application.Comment: 8 pages, 10 figures, submitted to PR

Microphotoluminescence spectroscopy of vertically stacked In x Ga 1 − x A s / G a A s quantum wires

Disorder and spectral broadening of vertically stacked InGaAs/GaAs V-grooved quantum wires have been investigated by means of microprobe luminescence. We show that the main spectral broadening mechanism originates from monolayer fluctuations at the bottom of the wire. A direct evidence of monolayer height islands of area 40\ifmmode\times\else\texttimes\fi{}40\mathrm{nm} formed at the bottom of the grooves is provided by atomic force microscopy. Lateral and vertical wire-to-wire fluctuations are found to be negligible on the micron scale

Ultra-strong light–matter coupling for designer Reststrahlen band

The strength of the light–matter interaction depends on the number of dipoles that can couple with the photon trapped in an optical cavity. The coupling strength can thus be maximized by filling the entire cavity volume with an ensemble of interacting dipoles. In this work this is achieved by inserting a highly doped semiconductor layer in a subwavelength plasmonic resonator. In our system the ultra-strong light–matter coupling occurs between a collective electronic excitation and the cavity photon. The measured coupling strength is 73% of the matter excitation energy, the highest ever reported for a light–matter coupled system at room temperature. We experimentally and theoretically demonstrate that such an ultra-strong interaction modifies the optical properties on a very wide spectral range (20–250 meV), and results in the appearance of a photonic gap of 38 meV, independently of the light polarization and angle of incidence. Light–matter ultra-strong coupling can thus be exploited to conceive metasurfaces with an engineered reflectivity band

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 demonstrate 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 a semiconductor absorber based on the collective electronic excitation in a two dimensional electron gas. The optimized electric field confinement is exhibited by the observation of the ultra-strong light-matter coupling regime, and opens many possible applications for these structures in detectors, modulators and sources of THz radiation

Recommendation of RILEM TC 261-CCF: test method to determine the flexural creep of fibre reinforced concrete in the cracked state

[EN] To date there is no clear consensus about how creep of cracked FRC structural elements should be considered. In recent years, different methodologies have been developed for multiple stress cases. The absence of a standardised methodology to evaluate flexural creep in the cracked state has hindered general comparisons and conclusions that could lead to significant advances in this topic. Since 2014, the study of the creep behaviour of cracked FRC has been coordinated by the RILEM TC 261-CCF. All the available creep methodologies were analysed in terms of procedure, equipment and results. A comprehensive Round-Robin Test (RRT) on the creep behaviour of cracked sections of FRC was proposed and undertaken by a total of 19 participant laboratories from 14 countries all over the world. The analysis and conclusions of the RRT results and the different methodologies provided the basis for this recommendation. This recommendation focuses on the test method to evaluate the flexural creep of FRC specimens in the cracked state. Guidelines on specimen production, detailed test equipment, experimental setup and test procedure as well as the definitions of the most relevant parameters are provided.Llano-Torre, A.; Serna Ros, P. (2021). Recommendation of RILEM TC 261-CCF: test method to determine the flexural creep of fibre reinforced concrete in the cracked state. Materials and Structures. 54(3):1-20. https://doi.org/10.1617/s11527-021-01675-0S120543Theodorakopoulos D (1995) Creep characteristics of glass reinforced cement under flexural loading. Cement Concr Compos 17:267–279Chanvillard G, Roque O (1999) Behaviour of fibre reinforced concrete cracked section under sustained load. High Performance Fiber Reinforced Cement Composites (HPFRCC 3) Mainz, Germany, pp 239–250, RILEM PRO 06Kurt S, Balaguru P (2000) Post crack creep of polymeric fibre-reinforced concrete in flexure. Cem Concr Res 30(2):183–190Mackay J, Trottier JF (2004) Post-crack behavior of steel and synthetic FRC under flexural creep. In: Shotcrete, Proc. 2nd Intnl. Conf. on Engineering, Cairns, Australia (2004), pp 183–192Kusterle W (2009) Viscous material behaviour of solids- creep of polymer fibre reinforced concrete. In: Proc. 5th Central European Congress on Concrete Engineering. obv, Baden, pp 95–100Arango S, Serna P, Martí-Vargas JR, García-Taengua E (2012) A test method to characterize flexural creep behaviour of pre-cracked FRC specimens. Exp Mech 52(8):1067–1078Zerbino RL, Barragan BE (2012) Long-term behaviour of cracked steel fibre-reinforced concrete beams under sustained loading. ACI Mater J 109(2):215–224Abrishambaf A, Barros JAO, Cunha VMCF (2015) Time-dependent flexural behaviour of cracked steel fibre reinforced self-compacting concrete panels. Cem Concr Res 72:21–36Buratti N, Mazzotti C (2016) Experimental tests on the long-term behaviour of SFRC and MSFRC in bending and direct tension. In: Proceedings of the BEFIB 2016, 9th RILEM international symposium on fiber reinforced concrete, pp. 163–174, Vancouver, Canada, 19–21 Sept 2016Babafemi AJ, Boshoff WP (2015) Tensile creep of macro-synthetic fibre reinforced concrete (MSFRC) under uni-axial tensile loading. Cement Concr Compos 55:62–69Vrijdaghs R, di Prisco M, Vandewalle L (2018) Uniaxial tensile creep of a cracked polypropylene fiber reinforced concrete. Mater Struct 51:5. https://doi.org/10.1617/s11527-017-1132-5Vasanelli E, Micelli F, Aiello MA, Plizzari G (2013) Long term behaviour of FRC flexural beams under sustained load. Eng Struct 56:1858–1867Bernard ES (2010) Influence of fibre type on creep deformation of cracked fibre-reinforced shotcrete panels. ACI Mater J 107(5):474–480EFNARC (2012) Testing sprayed concrete—Creep test on square panelLarive C, Rogat D, Chamoley D, Regnard A, Pannetier T, Thuaud C (2016) Influence of fibres on the creep behaviour of reinforced sprayed concrete. In: Proceedings of ITA World Tunnel Congress WTC 2016, April 22‐28, San Francisco, United StatesMonetti DH, Llano-Torre A, Torrijos MC, Giaccio G, Zerbino R, Martí-Vargas JR, Serna P (2019) Long-term behavior of cracked fiber reinforced concrete under service conditions. Construct Build Mater; 196:649–658. https://doi.org/10.1016/j.conbuildmat.2018.10.230Llano-Torre A., Martí-Vargas JR, Serna P (2020) Flexural and compressive creep behavior of UHPFRC specimens. Construct Build Mater; 244:118254. https://doi.org/10.1016/j.conbuildmat.2020.118254Serna P, Llano-Torre A and Cavalaro S H P (ed) (2017) Creep behaviour in cracked sections of fibre reinforced concrete: proceedings of the international RILEM Workshop FRC-CREEP 2016. RILEM bookseries 14 (Dordrecht: Springer)Llano-Torre A, Serna P, Cavalaro SHP (2016) International round robin test on creep behavior of FRC supported by the RILEM TC 261-CCF. In: Proceedings of the BEFIB 2016, 9th RILEM international symposium on fiber reinforced concrete, pp 127–140, Vancouver, Canada, 19–21 Sept 2016Serna P, Llano-Torre A, García-Taengua E, Martí-Vargas JR (2015) Database on the long-term behaviour of FRC: a useful tool to achieve overall conclusions. In: Proceedings of the 10th international conference on mechanics and physics of Creep, Shrinkage, and Durability of Concrete and Concrete Structures, Vienna, September 2015, pp 1544–1553Llano-Torre A., Serna P. (eds) Round-Robin test on creep behaviour in cracked sections of FRC: experimental program, results and database analysis. RILEM State-of-the-Art Reports. Springer. https://doi.org/10.1007/978-3-030-72736-9ASTM International (2015) C1812/C1812M-15e1 Standard Practice for Design of Journal Bearing Supports to be Used in Fiber Reinforced Concrete Beam Tests. West Conshohocken, PA; ASTM International. https://doi.org/10.1520/C1812_C1812M-15E0