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  • Journal article
    Bertone G, Buchmueller OL, Cole PS, 2023,

    Perspectives on fundamental cosmology from Low Earth Orbit and the Moon

    , npj Microgravity, Vol: 9

    The next generation of space-based experiments will go hunting for answers to cosmology’s key open questions which revolve around inflation, dark matter and dark energy. Low earth orbit and lunar missions within the European Space Agency’s Human and Robotic Exploration programme can push our knowledge forward in all of these three fields. A radio interferometer on the Moon, a cold atom interferometer in low earth orbit and a gravitational wave interferometer on the Moon are highlighted as the most fruitful missions to plan and execute in the mid-term.

  • Journal article
    Chen Y, Wang K, Kadic M, Guenneau S, Wang C, Wegener Met al., 2023,

    Phonon transmission through a nonlocal metamaterial slab

    , Communications Physics, Vol: 6

    Previous theory and experiment has shown that introducing strong (nonlocal) beyond-nearest-neighbor interactions in addition to (local) nearest-neighbor interactions into rationally designed periodic lattices called metamaterials can lead to unusual wave dispersion relations of the lowest band. For roton-like dispersions, this especially includes the possibility of multiple solutions for the wavenumber at a given frequency. Here, we study the one-dimensional frequency-dependent acoustical phonon transmission of a slab of such nonlocal metamaterial in a local surrounding. In addition to the usual Fabry-Perot resonances, we find a series of bound states in the continuum. In their vicinity, sharp Fano-type transmission resonances occur, with sharp zero-transmission minima next to sharp transmission maxima. Our theoretical discussion starts with a discrete mass-and-spring model. We compare these results with solutions of a generalized wave equation for heterogeneous nonlocal effective media. We validate our findings by numerical calculations on three-dimensional metamaterial microstructures for one-dimensional acoustical wave propagation.

  • Journal article
    Lemkalli B, Kadic M, El Badri Y, Guenneau S, Bouzid A, Achaoui Yet al., 2023,

    Mapping of elastic properties of twisting metamaterials onto micropolar continuum using static calculations

    , International Journal of Mechanical Sciences, Vol: 254, ISSN: 0020-7403

    Recent developments in the engineering of metamaterials have brought forth a myriad of mesmerizing mechanical properties that do not exist in ordinary solids. Among these, twisting metamaterials and acoustical chirality are sample-size dependent. The purpose of this work is, first, to examine the mechanical performance of a new twisting cubic metamaterial. Then, we perform a comparative investigation of its twisting behavior using the finite element method on microstructure elements computation, a phenomenological model, and we compare them to the Eringen micropolar continuum, for which we enunciate a straightforward approach for retrieving effective parameters using static computations. Notably, the results of the three models are in good qualitative and quantitative agreements. Finally, a systematic comparison of dispersion relations was made for the continuum and for the microstructures with different sizes in unit cells as final proof of perfect mapping.

  • Journal article
    Araújo HM, Balashov SN, Borg JE, Brunbauer FM, Cazzaniga C, Frost CD, Garcia F, Kaboth AC, Kastriotou M, Katsioulas I, Khazov A, Kraus H, Kudryavtsev VA, Lilley S, Lindote A, Loomba D, Lopes MI, Asamar EL, Dapica PL, Majewski PA, Marley T, McCabe C, Mills AF, Nakhostin M, Neep T, Neves F, Nikolopoulos K, Oliveri E, Ropelewski L, Tilly E, Solovov VN, Sumner TJ, Tarrant J, Turnley R, van der Grinten MGD, Veenhof Ret al., 2023,

    The MIGDAL experiment: Measuring a rare atomic process to aid the search for dark matter

    , Astroparticle Physics, Vol: 151, ISSN: 0927-6505

    We present the Migdal In Galactic Dark mAtter expLoration (MIGDAL) experiment aiming at the unambiguous observation and study of the so-called Migdal effect induced by fast-neutron scattering. It is hoped that this elusive atomic process can be exploited to enhance the reach of direct dark matter search experiments to lower masses, but it is still lacking experimental confirmation. Our goal is to detect the predicted atomic electron emission which is thought to accompany nuclear scattering with low, but calculable, probability, by deploying an Optical Time Projection Chamber filled with a low-pressure gas based on CF4. Initially, pure CF4 will be used, and then in mixtures containing other elements employed by leading dark matter search technologies — including noble species, plus Si and Ge. High resolution track images generated by a Gas Electron Multiplier stack, together with timing information from scintillation and ionisation readout, will be used for 3D reconstruction of the characteristic event topology expected for this process — an arrangement of two tracks sharing a common vertex, with one belonging to a Migdal electron and the other to a nuclear recoil. Different energy-loss rate distributions along both tracks will be used as a powerful discrimination tool against background events. In this article we present the design of the experiment, informed by extensive particle and track simulations and detailed estimations of signal and background rates. In pure CF4 we expect to observe 8.9 (29.3) Migdal events per calendar day of exposure to an intense D–D (D–T) neutron generator beam at the NILE facility located at the Rutherford Appleton Laboratory (UK). With our nominal assumptions, 5σ median discovery significance can be achieved in under one day with either generator.

  • Journal article
    Williams RG, Ceppi P, Roussenov V, Katavouta A, Meijers AJSet al., 2023,

    The role of the Southern Ocean in the global climate response to carbon emissions.

    , Philos Trans A Math Phys Eng Sci, Vol: 381

    The effect of the Southern Ocean on global climate change is assessed using Earth system model projections following an idealized 1% annual rise in atmospheric CO2. For this scenario, the Southern Ocean plays a significant role in sequestering heat and anthropogenic carbon, accounting for 40% ± 5% of heat uptake and 44% ± 2% of anthropogenic carbon uptake over the global ocean (with the Southern Ocean defined as south of 36°S). This Southern Ocean fraction of global heat uptake is however less than in historical scenarios with marked hemispheric contrasts in radiative forcing. For this idealized scenario, inter-model differences in global and Southern Ocean heat uptake are strongly affected by physical feedbacks, especially cloud feedbacks over the globe and surface albedo feedbacks from sea-ice loss in high latitudes, through the top-of-the-atmosphere energy balance. The ocean carbon response is similar in most models with carbon storage increasing from rising atmospheric CO2, but weakly decreasing from climate change with competing ventilation and biological contributions over the Southern Ocean. The Southern Ocean affects a global climate metric, the transient climate response to emissions, accounting for 28% of its thermal contribution through its physical climate feedbacks and heat uptake, and so affects inter-model differences in meeting warming targets. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

  • Journal article
    Meine DCA, Vvedensky DD, 2023,

    Emergence of speculation in a hierarchical agent-based model

    , Physica A: Statistical Mechanics and its Applications, Vol: 620, ISSN: 0378-4371

    The Lux–Marchesi model has been modified to include hierarchical interactions to enable the examination of the effect of hierarchies on the formation of speculative bubbles. The Lux–Marchesi model includes two types of traders: fundamentalists and chartists, with the latter classified as either optimists or pessimists. The stock price is then determined by the number of fundamentalists and chartists who drive the supply and demand for the stock. This model produces volatility clustering and fat-tailed distributions seen in actual markets. Hierarchical interactions are based on communications between traders which successively influence higher levels of the hierarchy up to investment banks, governments, and currency blocks. The combination of the two models reproduces known characteristics of stock markets, including spontaneous bubbles and crashes. For certain hierarchy strengths, traders tend to a uniform opinion and an emergence of speculation can be observed. In this regime crashes happen.

  • Journal article
    Taylor JR, 2023,

    Early optical soliton research at Imperial College London

    , Optics Communications, Vol: 536, ISSN: 0030-4018

    The early work of the Femtosecond Optics Group at Imperial College on optical soliton generation in fibres is reviewed that commenced with studies of ultrashort pulse generation using high order soliton compression for the production of pulses of 18 fs. Also described are seminal studies of soliton Raman generation using long pulse pumping where evolution from modulational instability led to continuum generation and tunable femtosecond generation. Early investigations of seeding modulational instability for enhanced soliton generation and spectral extension are described, as is the work on seeding of noise, soliton generation from noise bursts and soliton generation from amplified noise bursts. The first study of femtosecond soliton amplification in Er fibre amplifiers is described as well as synchronous Raman amplification of solitons. Various schemes reviewing our investigations of adiabatic soliton compression and amplification are included for the generation of pulsewidth and wavelength tunable soliton sources in fully fibre integrated geometries.

  • Journal article
    Brun M, Guenneau S, 2023,

    Transformation design of in-plane elastic cylindrical cloaks, concentrators and lenses

    , WAVE MOTION, Vol: 119, ISSN: 0165-2125
  • Journal article
    Guo N-J, Li S, Liu W, Yang Y-Z, Zeng X-D, Yu S, Meng Y, Li Z-P, Wang Z-A, Xie L-K, Ge R-C, Wang J-F, Li Q, Xu J-S, Wang Y-T, Tang J-S, Gali A, Li C-F, Guo G-Cet al., 2023,

    Coherent control of an ultrabright single spin in hexagonal boron nitride at room temperature.

    , Nat Commun, Vol: 14

    Hexagonal boron nitride (hBN) is a remarkable two-dimensional (2D) material that hosts solid-state spins and has great potential to be used in quantum information applications, including quantum networks. However, in this application, both the optical and spin properties are crucial for single spins but have not yet been discovered simultaneously for hBN spins. Here, we realize an efficient method for arraying and isolating the single defects of hBN and use this method to discover a new spin defect with a high probability of 85%. This single defect exhibits outstanding optical properties and an optically controllable spin, as indicated by the observed significant Rabi oscillation and Hahn echo experiments at room temperature. First principles calculations indicate that complexes of carbon and oxygen dopants may be the origin of the single spin defects. This provides a possibility for further addressing spins that can be optically controlled.

  • Journal article
    Oulton R, 2023,

    Emission enhancement of erbium in a reverse nanofocusing waveguide

    , Nature Communications, Vol: 14, Pages: 1-10, ISSN: 2041-1723

    Since Purcell’s seminal report 75 years ago, electromagnetic resonators have been used to control light-matter interactions to make brighter radiation sources and unleash unprecedented control over quantum states of light and matter. Indeed, optical resonators such as microcavities and plasmonic antennas offer excellent control but only over a limited spectral range. Strategies to mutually tune and match emission and resonator frequency are often required, which is intricate and precludes the possibility of enhancing multiple transitions simultaneously. In this letter, we report a strong radiative emission rate enhancement of Er3+-ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. Remarkably, the large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions, which are typically only observed under cryogenic conditions. Simultaneous radiative emission enhancement of multiple quantum states is of great interest for photonic quantum networks and on-chip data communications.

  • Journal article
    Kerridge-Johns WR, Srinivasa Rao A, Fujimoto Y, Omatsu Tet al., 2023,

    Red, orange, and dual wavelength vortex emission from Pr:WPFGF fiber laser using a microscope slide output coupler.

    , Opt Express, Vol: 31, Pages: 16607-16614

    Visible vortex beams have a large array of applications; however, the sources are often large or complex. Here, we present a compact vortex source with red, orange, and dual wavelength emission. This Pr:Waterproof Fluoro-Aluminate Glass fiber laser uses a standard microscope slide as an interferometric output coupler, yielding high quality first order vortex modes in a compact setup. We further demonstrate the broad (∼5 nm) emission bands in the orange (610 nm), red (637 nm) and near-infrared regions (698 nm), with the potential for green (530 nm) and cyan (485 nm) emission. This is a low-cost, compact and accessible device giving high quality modes for visible vortex applications.

  • Journal article
    Smith M, Sparks H, Almagro J, Chaigne A, Behrens A, Dunsby C, Salbreux Get al., 2023,

    Active mesh and neural network pipeline for cell aggregate segmentation

    , Biophysical Journal, Vol: 122, Pages: 1586-1599, ISSN: 0006-3495

    Segmenting cells within cellular aggregates in 3D is a growing challenge in cell biology due to improvements in capacity and accuracy of microscopy techniques. Here, we describe a pipeline to segment images of cell aggregates in 3D. The pipeline combines neural network segmentations with active meshes. We apply our segmentation method to cultured mouse mammary gland organoids imaged over 24 h with oblique plane microscopy, a high-throughput light-sheet fluorescence microscopy technique. We show that our method can also be applied to images of mouse embryonic stem cells imaged with a spinning disc microscope. We segment individual cells based on nuclei and cell membrane fluorescent markers, and track cells over time. We describe metrics to quantify the quality of the automated segmentation. Our segmentation pipeline involves a Fiji plugin that implements active mesh deformation and allows a user to create training data, automatically obtain segmentation meshes from original image data or neural network prediction, and manually curate segmentation data to identify and correct mistakes. Our active meshes-based approach facilitates segmentation postprocessing, correction, and integration with neural network prediction.

  • Journal article
    Hall G, Grillo AA, 2023,

    ASICs for LHC intermediate tracking detectors

    , Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol: 1050, ISSN: 0168-9002

    The tracking detectors proposed for the LHC were unprecedented in their size and operational requirements, especially radiation tolerance and data rates. When they were first envisaged it was uncertain that technologies would be available which would meet the specifications, and considerable R&D was necessary to demonstrate this. In particular, customised electronic integrated circuits were evidently essential, yet they were probably technologically the least certain components. The radiation levels and the readout rates in earlier generations of collider experiments were far below those required for the LHC trackers and the number of LHC readout chips required was much larger. Nevertheless, solutions were eventually found, which continue to function reliably with excellent performance. In many ways, the tracker ASIC developments laid foundations and blazed trails for chips later designed for many other sub-detector systems. The ATLAS and CMS trackers developed different solutions to the LHC challenges, and are representative of other LHC systems. This review focuses on the ASIC developments undertaken by these two experiments to explain the most important innovations, recent progress and future challenges. The term “intermediate tracking detectors” is meant to differentiate from the innermost trackers close to the beam pipe and interaction region. This region is served by pixel detectors, whose development began later than the LHC trackers discussed here.

  • Journal article
    Jeong S, Rana A, Kim J-H, Qian D, Park K, Jang J-H, Luke J, Kwon S, Kim J, Tuladhar PS, Kim J-S, Lee K, Durrant JR, Kang Het al., 2023,

    New ternary blend strategy based on a vertically self-assembled passivation layer enabling efficient and photostable inverted organic solar cells

    , Advanced Science, Pages: 1-9, ISSN: 2198-3844

    Herein, a new ternary strategy to fabricate efficient and photostable inverted organic photovoltaics (OPVs) is introduced by combining a bulk heterojunction (BHJ) blend and a fullerene self-assembled monolayer (C60 -SAM). Time-of-flight secondary-ion mass spectrometry - analysis reveals that the ternary blend is vertically phase separated with the C60 -SAM at the bottom and the BHJ on top. The average power conversion efficiency - of OPVs based on the ternary system is improved from 14.9% to 15.6% by C60 -SAM addition, mostly due to increased current density (Jsc ) and fill factor -. It is found that the C60 -SAM encourages the BHJ to make more face-on molecular orientation because grazing incidence wide-angle X-ray scattering - data show an increased face-on/edge-on orientation ratio in the ternary blend. Light-intensity dependent Jsc data and charge carrier lifetime analysis indicate suppressed bimolecular recombination and a longer charge carrier lifetime in the ternary system, resulting in the enhancement of OPV performance. Moreover, it is demonstrated that device photostability in the ternary blend is enhanced due to the vertically self-assembled C60 -SAM that successfully passivates the ZnO surface and protects BHJ layer from the UV-induced photocatalytic reactions of the ZnO. These results suggest a new perspective to improve both performance and photostability of OPVs using a facial ternary method.

  • Journal article
    Cael BB, Bloch-Johnson J, Ceppi P, Fredriksen H-B, Goodwin P, Gregory JM, Smith CJ, Williams RGet al., 2023,

    Energy budget diagnosis of changing climate feedback.

    , Sci Adv, Vol: 9

    The climate feedback determines how Earth's climate responds to anthropogenic forcing. It is thought to have been more negative in recent decades due to a sea surface temperature "pattern effect," whereby warming is concentrated in the western tropical Pacific, where nonlocal radiative feedbacks are very negative. This phenomenon has however primarily been studied within climate models. We diagnose a pattern effect from historical records as an evolution of the climate feedback over the past five decades. Our analysis assumes a constant rate of change of the climate feedback, which is justified post hoc. We find a decrease in climate feedback by 0.8 ± 0.5 W m-2 K-1 over the past 50 years, corresponding to a reduction in climate sensitivity. Earth system models' climate feedbacks instead increase over this period. Understanding and simulating this historical trend and its future evolution are critical for reliable climate projections.

  • Journal article
    Chaumet PC, Guenneau SRL, 2023,

    Electromagnetic forces on a discrete concentrator under time-harmonic illumination

    , Applied Physics Letters, Vol: 122, ISSN: 0003-6951

    We study electromagnetic forces and torques experienced on both perfect and discretized transformation-based concentrators, under time-harmonic illumination. The effect of the concentration is investigated in both cases and compared to the case of a perfect cloak. The effect of a Lorentz dispersion model on the optical force and torque is also investigated, and the force experienced by a dielectric particle located at the center of the concentrator is studied.

  • Journal article
    Yang Y-Z, Zhu T-X, Li Z-P, Zeng X-D, Guo N-J, Yu S, Meng Y, Wang Z-A, Xie L-K, Zhou Z-Q, Li Q, Xu J-S, Gao X-Y, Liu W, Wang Y-T, Tang J-S, Li C-F, Guo G-Cet al., 2023,

    Laser Direct Writing of Visible Spin Defects in Hexagonal Boron Nitride for Applications in Spin-Based Technologies

    , ACS Applied Nano Materials, Vol: 6, Pages: 6407-6414, ISSN: 2574-0970
  • Journal article
    Montgomery J, Ebert R, Allegrini F, Bagenal F, Bolton S, DiBraccio G, Fuselier S, Wilson R, Masters Aet al., 2023,

    Investigating the occurrence of Kelvin-Helmholtz instabilities at Jupiter’s dawn magnetopause

    , Geophysical Research Letters, ISSN: 0094-8276
  • Journal article
    Cohen L, 2023,

    Landau theory-based relaxational modelling of first-order magnetic transition dynamics in magnetocaloric materials

    , Journal of Physics D: Applied Physics, Vol: 56, Pages: 1-9, ISSN: 0022-3727

    The magnetocaloric effect is often largest within the neighborhood of a first-order phase transition. This effect can be utilized in magnetocaloric refrigeration, which completely eliminates the need for the greenhouse gases utilized in conventional refrigeration. However, such transitions present unique dynamical effects and are accompanied by hysteresis, which can be detrimental for such refrigeration applications. In this work, a Landau theory-based relaxational model is used to study the magnetic hysteresis and dynamics of the first-order magnetic transition of LaFe13−xSix. Fitting the experimental magnetization data as a function of applied magnetic field under different field sweep rates with this model provided the Landau parameters (A, B, and C) and the kinetic coefficient of the studied material. We demonstrate the tendency of the magnetic hysteresis to increase with the magnetic field sweep rate, underlining the importance of studying and minimizing the magnetic hysteresis in magnetic refrigerants at practical field sweep rates. While evaluating the temperature dependence of the time required for a complete transition to occur, a nonmonotonic behavior and a sharp peak were found for temperatures near the transition temperature. Such peaks occur at the same temperature as the peak of the magnetic entropy change for low fields, whereas for higher fields the two peaks decouple. This information is critical for technological applications (such as refrigerators/heat pumps) as it provides guidelines for the optimization of the magnetic field amplitude in order to reduce the transition timescale and consequently maximize the machine operational frequency and amount of heat that is pumped in/out per second.

  • Journal article
    Berté R, Weber T, de Souza Menezes L, Kühner L, Aigner A, Barkey M, Wendisch FJ, Kivshar Y, Tittl A, Maier SAet al., 2023,

    Permittivity-Asymmetric Quasi-Bound States in the Continuum.

    , Nano Lett, Vol: 23, Pages: 2651-2658

    Breaking the in-plane geometric symmetry of dielectric metasurfaces allows us to access a set of electromagnetic states termed symmetry-protected quasi-bound states in the continuum (qBICs). Here we demonstrate that qBICs can also be accessed by a symmetry breaking in the permittivity of the comprising materials. While the physical size of atoms imposes a limit on the lowest achievable geometrical asymmetry, weak permittivity modulations due to carrier doping, and electro-optical Pockels and Kerr effects, usually considered insignificant, open the possibility of infinitesimal permittivity asymmetries for on-demand, dynamically tunable resonances of extremely high quality factors. As a proof-of-principle, we probe the excitation of permittivity-asymmetric qBICs (ε-qBICs) using a prototype Si/TiO2 metasurface, in which the asymmetry in the unit cell is provided by the permittivity contrast of the materials. ε-qBICs are also numerically demonstrated in 1D gratings, where quality-factor enhancement and tailored interference phenomena of qBICs are shown via the interplay of geometrical and permittivity asymmetries.

  • Journal article
    Xiao X, Gillibert R, Foti A, Coulon P-E, Ulysse C, Levato T, Maier SA, Giannini V, Gucciardi PG, Rizza Get al., 2023,

    Plasmonic Polarization Rotation in SERS Spectroscopy.

    , Nano Lett, Vol: 23, Pages: 2530-2535

    Surface-enhanced Raman optical activity (SEROA) has been extensively investigated due to its ability to directly probe stereochemistry and molecular structure. However, most works have focused on the Raman optical activity (ROA) effect arising from the chirality of the molecules on isotropic surfaces. Here, we propose a strategy for achieving a similar effect: i.e., a surface-enhanced Raman polarization rotation effect arising from the coupling of optically inactive molecules with the chiral plasmonic response of metasurfaces. This effect is due to the optically active response of metallic nanostructures and their interaction with molecules, which could extend the ROA potential to inactive molecules and be used to enhance the sensibility performances of surface-enhanced Raman spectroscopy. More importantly, this technique does not suffer from the heating issue present in traditional plasmonic-enhanced ROA techniques, as it does not rely on the chirality of the molecules.

  • Journal article
    Rego L, Smirnova O, Ayuso Molinero D, 2023,

    Tilting light's polarization plane to spatially separate the ultrafast nonlinear response of chiral molecules

    , Nanophotonics, Pages: 1-7, ISSN: 2192-8606

    Distinguishing between the left- and right-handed versions of a chiral molecule (enantiomers) is vital, but also inherently difficult. Traditional optical methods using elliptically/circularly polarized light rely on linear effects which arise beyond the electric-dipole approximation, posing major limitations for ultrafast spectroscopy. Here we show how to turn an ultrashort elliptical pulse into an efficient chiro-optical tool: by tilting its polarization plane towards its propagation direction. This forward tilt can be achieved by focusing the beam tightly, creating structured light which exhibits a nontrivial polarization pattern in space. Using state-of-the-art computational modelling, we show that our structured field realizes a near-field interferometer for efficient chiral recognition that separates the nonlinear optical response of left- and right-handed molecules in space. Our work provides a simple, yet highly efficient, way of spatially structuring the polarization of light to image molecular chirality, with extreme enantio-efficiency and on ultrafast time scales.

  • Journal article
    Lee TH, Fu Y, Chin Y-C, Pacalaj R, Labanti C, Park SY, Dong Y, Cho HW, Kim JY, Minami D, Durrant JR, Kim J-Set al., 2023,

    Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance

    , Nature Communications, Vol: 14, Pages: 1-12, ISSN: 2041-1723

    The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs.

  • Journal article
    Abdelwahab I, Tilmann B, Zhao X, Verzhbitskiy I, Berté R, Eda G, Wilson WL, Grinblat G, de S Menezes L, Loh KP, Maier SAet al., 2023,

    Highly Efficient Sum-Frequency Generation in Niobium Oxydichloride NbOCl<inf>2</inf> Nanosheets

    , Advanced Optical Materials, Vol: 11

    Parametric infrared (IR) upconversion is a process in which low-frequency IR photons are upconverted into high-frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer-scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum-frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross-correlator for ultrashort pulse characterization.

  • Journal article
    Tirole R, Vezzoli S, Galiffi E, Robertson I, Maurice D, Tilmann B, Maier SA, Pendry JB, Sapienza Ret al., 2023,

    Double-slit time diffraction at optical frequencies

    , NATURE PHYSICS, ISSN: 1745-2473
  • Journal article
    Garratt TK, Geach JE, Tamura Y, Coppin KEK, Franco M, Ao Y, Chen CC, Cheng C, Clements DL, Dai YS, Dannerbauer H, Greve TR, Hatsukade B, Hwang HS, Jiang L, Kohno K, Koprowski MP, Michałowski MJ, Sawicki M, Scott D, Shim H, Takeuchi TT, Wang WH, Xue YQ, Yang Cet al., 2023,

    The SCUBA-2 Large eXtragalactic Survey: 850 μm map, catalogue and the bright-end number counts of the XMM-LSS field

    , Monthly Notices of the Royal Astronomical Society, Vol: 520, Pages: 3669-3687, ISSN: 0035-8711

    We present 850 μm imaging of the XMM-LSS field observed for 170 h as part of the James Clerk Maxwell Telescope SCUBA-2 Large eXtragalactic Survey (S2LXS). S2LXS XMM-LSS maps an area of 9 deg2, reaching a moderate depth of 1σ 4 mJy beam−1. This is the largest contiguous area of extragalactic sky mapped by James Clerk Maxwell Telescope (JCMT) at 850 μm to date. The wide area of the S2LXS XMM-LSS survey allows us to probe the ultra-bright (S850μm 15 mJy), yet rare submillimetre population. We present the S2LXS XMM-LSS catalogue, which comprises 40 sources detected at >5σ significance, with deboosted flux densities in the range of 7–48 mJy. We robustly measure the bright-end of the 850 μm number counts at flux densities >7 mJy, reducing the Poisson errors compared to existing measurements. The S2LXS XMM-LSS observed number counts show the characteristic upturn at bright fluxes, expected to be motivated by local sources of submillimetre emission and high-redshift strongly lensed galaxies. We find that the observed 850 μm number counts are best reproduced by model predictions that include either strong lensing or source blending from a 15-arcsec beam, indicating that both may make an important contribution to the observed overabundance of bright single dish 850 μm selected sources. We make the S2LXS XMM-LSS 850 μm map and >5σ catalogue presented here publicly available.

  • Journal article
    Šafránková J, Němeček Z, Němec F, Verscharen D, Horbury TS, Bale SD, Přech Let al., 2023,

    Evolution of Magnetic Field Fluctuations and Their Spectral Properties within the Heliosphere: Statistical Approach

    , Astrophysical Journal Letters, Vol: 946, ISSN: 2041-8205

    We present the first comprehensive statistical study of the evolution of compressive and noncompressive magnetic field fluctuations in the inner heliosphere. Based on Parker Solar Probe (PSP) and Solar Orbiter data at various distances from the Sun, we show the general trends and compare them with Wind observations near 1 au. The paper analyzes solar wind power spectra of magnetic field fluctuations in the inertial and kinetic ranges of frequencies. We find a systematic steepening of the spectrum in the inertial range with the spectral index of around −3/2 at closest approach to the Sun toward −5/3 at larger distances (above 0.4 au), the spectrum of the field component perpendicular to the background field being steeper at all distances. In the kinetic range, the spectral indices increase with distance from −4.8 at closest PSP approach to ≈−3 at 0.4 au and this value remains approximately constant toward 1 au. We show that the radial profiles of spectral slopes, fluctuation amplitudes, spectral breaks, and their mutual relations undergo rapid changes near 0.4 au.

  • Journal article
    Rendell-Bhatti F, Zeng M, Lloveras P, Tamarit J-L, Barrio M, Connolly ET, MacLaren DA, Johnson F, Cohen LF, Boldrin Det al., 2023,

    Improving barocaloric properties by tailoring transition hysteresis in Mn₃Cu₁-ₓSnₓN antiperovskites

    , JPhys Energy, Vol: 5, Pages: 1-10, ISSN: 2515-7655

    The magnetically frustrated manganese nitride antiperovskite family displays significant changes of entropy under changes in hydrostatic pressure near a first-order antiferromagnetic to paramagnetic phase transition that can be useful for the emerging field of solid-state barocaloric cooling. In previous studies, the transition hysteresis has significantly reduced the reversible barocaloric effects (BCE). Here we show that the transition hysteresis can be tailored through quaternary alloying in the Mn3Cu$_{1-x}$Sn$_{x}$N system. We find the magnitude of hysteresis is minimised when Cu and Sn are equiatomic (x = 0.5) reaching values far less than previously found for Mn3AN ($A = $ Pd, Ni, Ga, Zn), whilst retaining entropy changes of the same order of magnitude. These results demonstrate that reversible BCE are achievable for p < 100 MPa in the Mn3(A, B)N family and suggest routes to modify the transition properties in compounds of the same family.

  • Journal article
    Coste N, Gundin M, Fioretto DA, Thomas SE, Millet C, Mehdi E, Somaschi N, Morassi M, Pont M, Lemaître A, Belabas N, Krebs O, Lanco L, Senellart Pet al., 2023,

    Probing the dynamics and coherence of a semiconductor hole spin via acoustic phonon-assisted excitation

    , Quantum Science and Technology, Vol: 8

    Spins in semiconductor quantum dots (QDs) are promising local quantum memories to generate polarization-encoded photonic cluster states, as proposed in the pioneering Lindner and Rudolph scheme (2009 Phys. Rev. Lett. 103 113602). However, harnessing the polarization degree of freedom of the optical transitions is hindered by resonant excitation schemes that are widely used to obtain high photon indistinguishability. Here we show that acoustic phonon-assisted excitation, a scheme that preserves high indistinguishability, also allows to fully exploit the polarization selective optical transitions to initialise and measure single spin states. We access the coherence of hole spin systems in a low transverse magnetic field and directly monitor the spin Larmor precession both during the radiative emission process of an excited state or in the QD ground state. We report a spin state detection fidelity of 94.7±0.2% granted by the optical selection rules and a 25±5 ns hole spin coherence time, demonstrating the potential of this scheme and system to generate linear cluster states with a dozen of photons.

  • Journal article
    Seo H, O'Neill LW, Bourassa MA, Czaja A, Drushka K, Edson JB, Fox-Kemper B, Frenger I, Gille ST, Kirtman BP, Minobe S, Pendergrass AG, Renault L, Roberts MJ, Schneider N, Small RJ, Stoffelen A, Wang Qet al., 2023,

    Ocean Mesoscale and Frontal-Scale Ocean-Atmosphere Interactions and Influence on Large-Scale Climate: A Review

    , Journal of Climate, Vol: 36, Pages: 1981-2013, ISSN: 0894-8755

    Two decades of high-resolution satellite observations and climate modeling studies have indicated strong ocean-atmosphere coupled feedback mediated by ocean mesoscale processes, including semipermanent and meandrous SST fronts, mesoscale eddies, and filaments. The air-sea exchanges in latent heat, sensible heat, momentum, and carbon dioxide associated with this so-called mesoscale air-sea interaction are robust near the major western boundary currents, Southern Ocean fronts, and equatorial and coastal upwelling zones, but they are also ubiquitous over the global oceans wherever ocean mesoscale processes are active. Current theories, informed by rapidly advancing observational and modeling capabilities, have established the importance of mesoscale and frontalscale air-sea interaction processes for understanding large-scale ocean circulation, biogeochemistry, and weather and climate variability. However, numerous challenges remain to accurately diagnose, observe, and simulate mesoscale air-sea interaction to quantify its impacts on large-scale processes. This article provides a comprehensive review of key aspects pertinent to mesoscale air-sea interaction, synthesizes current understanding with remaining gaps and uncertainties, and provides recommendations on theoretical, observational, and modeling strategies for future air-sea interaction research. modulate the air-sea exchanges in heat, momentum, and mass (e.g., gases such as water vapor and carbon dioxide), altering coupled boundary layer processes. Studies suggest that skillful simulations and predictions of ocean circulation, biogeochemistry, and weather events and climate variability depend on accurate representation of the eddy-mediated air-sea interaction. However, numerous challenges remain in accurately diagnosing, observing, and simulating mesoscale air-sea interaction to quantify its large-scale impacts. This article synthesizes the latest understanding of mesoscale air-sea interaction, identifies remaini

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