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Coherent Ising machines (CIMs) constitute a promising approach to solve computationally hard optimization problems by mapping them to ground state searches of the Ising model and implementing them with optical artificial spin-networks. However, while CIMs promise speed-ups over conventional digital computers, they are still challenging to build and operate. Here, we propose and test a concept for a fully programmable CIM, which is based on opto-electronic oscillators subjected to self-feedback. Contrary to current CIM designs, the artificial spins are generated in a feedback induced bifurcation and encoded in the intensity of coherent states. This removes the necessity for nonlinear optical processes or large external cavities and offers significant advantages regarding stability, size and cost. We demonstrate a compact setup for solving MAXCUT optimization problems on regular and frustrated graphs with 100 spins and can report similar or better performance compared to CIMs based on degenerate optical parametric oscillators., Coherent Ising machines are an unconventional optical computing architecture for solving optimization problems. Böhm et al. present a design based on opto-electronic feedback systems that avoids using nonlinear optical materials, improving the prospects for scalability and reliable operation.

In optical communications the transmission bandwidth of single mode optical fibers is almost fully exploited. To further increase the capacity of a telecommunication link, multiplexing techniques can be applied across 5 physical dimensions: amplitude, quadrature, polarization, frequency and space, with all but the latter being nearly exhausted. We experimentally demonstrate the feasibility of an original space division multiplexing technique based on the classification of speckle patterns measured at the fiber’s output. By coupling multiple optical signals into a standard multimode optical fiber, speckle patterns arise at the fiber’s end facet. This is due to quasi-random interference between the excited modes of propagation. We show how these patterns depend on the parameters of the optical signal beams and the fiber length. Classification of the speckle patterns allows the detection of the independent signals: we can detect the state (i.e. on or off ) of different beams that are multiplexed in the fiber. Our results show that the proposed space division multiplexing on standard multimode fibers is robust to mode-mixing and polarization scrambling effects.

Funding Information: This study was partly supported by the Centre National d’Études Spatiale (CNES) through the project “Hydrodynamics of wet foams". A.S. acknowledges Véronique Trappe and Eric Dufresne for interesting discussions. Publisher Copyright: © 2023, The Author(s). Foams are unstable jammed materials. They evolve over timescales comparable to their “time of use", which makes the study of their destabilisation mechanisms crucial for applications. In practice, many foams are made from viscoelastic fluids, which are observed to prolong their lifetimes. Despite their importance, we lack understanding of the coarsening mechanism in such systems. We probe the effect of continuous phase viscoelasticity on foam coarsening with foamed emulsions. We show that bubble size evolution is strongly slowed down and foam structure hugely impacted. The main mechanisms responsible are the absence of continuous phase redistribution and a non-trivial link between foam structure and mechanical properties. These combine to give spatially heterogeneous coarsening. Beyond their importance in the design of foamy materials, the results give a macroscopic vision of phase separation in a viscoelastic medium.

Lipid nanocapsules (NCs) represent promising tools in clinical practice for diagnosis and therapy applications. However, the NC appropriate functionalization is essential to guarantee high biocompatibility and molecule loading ability. In any medical application, the immune system-impact of differently functionalized NCs still remains to be fully understood. A comprehensive study on the action exerted on human peripheral blood mononuclear cells (PBMCs) and major immune subpopulations by three different NC coatings: pluronic, chitosan and polyethylene glycol-polylactic acid (PEG) is reported. After a deep particle characterization, the uptake was assessed by flow-cytometry and confocal microscopy, focusing then on apoptosis, necrosis and proliferation impact in T cells and monocytes. Cell functionality by cell diameter variations, different activation marker analysis and cytokine assays were performed. We demonstrated that the NCs impact on the immune cell response is strongly correlated to their coating. Pluronic-NCs were able to induce immunomodulation of innate immunity inducing monocyte activations. Immunomodulation was observed in monocytes and T lymphocytes treated with Chitosan-NCs. Conversely, PEG-NCs were completely inert. These findings are of particular value towards a pre-selection of specific NC coatings depending on biomedical purposes for pre-clinical investigations; i.e. the immune-specific action of particular NC coating can be excellent for immunotherapy applications.

Funding Information: We thank A. Upcher for assistance with transmission electron microscopy. We acknowledge the Swiss Light Source for providing synchrotron radiation facilities, and thank V. Olieric and T. Tomikazi for their assistance in using beamline PXI-X06SA. We thank D. Machlis, the BGU university photographer, for photographing the Lysmata amboinensis in the insert of Fig. . This work was performed using resources provided by the Cambridge Service for Data Driven Discovery (CSD3) operated by the University of Cambridge Research Computing Service ( www.csd3.cam.ac.uk ), provided by Dell EMC and Intel using Tier-2 funding from the Engineering and Physical Sciences Research Council (capital grant no. EP/T022159/1), and DiRAC funding from the Science and Technology Facilities Council ( www.dirac.ac.uk ). Funding was provided by an ERC Starting Grant (grant no. 852948, ‘CRYSTALEYES’) and an HFSP grant (grant no. RGP0037/2022) awarded to B.A.P. B.A.P. is the Nahum Guzik Presidential Recruit. B.A.P. is a recipient of the 2019 Azrieli Faculty Fellowship. Funding was also provided by the European Union’s Horizon 2020 research and innovation programme under a Marie Skłodowska-Curie grant agreement (no. 893136) and Academy of Finland grant (no. 347789) awarded to J.S.H. A Swiss National Science Foundation Grant (grant no. 40B1-0_198708) was awarded to L.S. Electron microscopy studies were supported by the Ilse Katz Institute for Nanoscale Science & Technology at Ben-Gurion University of the Negev. L.A. and D.O. acknowledge support from the Minerva Stiftung. | openaire: EC/H2020/893136/EU//MALDIP A fundamental question regarding light scattering is how whiteness, generated from multiple scattering, can be obtained from thin layers of materials. This challenge arises from the phenomenon of optical crowding, whereby, for scatterers packed with filling fractions higher than ~30%, reflectance is drastically reduced due to near-field coupling between the scatterers. Here we show that the extreme birefringence of isoxanthopterin nanospheres overcomes optical crowding effects, enabling multiple scattering and brilliant whiteness from ultra-thin chromatophore cells in shrimp. Strikingly, numerical simulations reveal that birefringence, originating from the spherulitic arrangement of isoxanthopterin molecules, enables intense broadband scattering almost up to the maximal packing for random spheres. This reduces the thickness of material required to produce brilliant whiteness, resulting in a photonic system that is more efficient than other biogenic or biomimetic white materials which operate in the lower refractive index medium of air. These results highlight the importance of birefringence as a structural variable to enhance the performance of such materials and could contribute to the design of biologically inspired replacements for artificial scatterers like titanium dioxide.

The combination of different polymers in the form of blended plastics has been used in the plastic industry for a long time. Nevertheless, analyses of microplastics (MPs) have been mainly limited to the study of particles made of single-type polymers. Accordingly, two members of the Polyolefins (POs) family, i.e., Polypropylene (PP) and Low-density Polyethylene (LDPE) are blended and extensively studied in this work due to their applications in industry as well as abundance in the environment. It is shown that 2-D Raman mapping only provides information about the surface of blended MPs (B-MPs). While complimentary 3-D volume analysis is needed to fully understand the presence of various polymers in such complex samples. Therefore, 3-D Raman mapping is applied to visualize the morphology of the distribution of polymers within the B-MPs together with the quantitative estimation of their concentrations. A parameter defined as the concentration estimate error (CEE) evaluates the precision of the quantitative analysis. Furthermore, the impact of four excitation wavelengths 405, 532, 633, and 785 nm is investigated on the obtained results. Finally, the application of a line-shaped laser beam profile (line-focus) is introduced for reducing the measurement time from 56 to 2 h.

Publisher Copyright: © 2023. The Author(s). The limited diversity in targets of available antibiotic therapies has put tremendous pressure on the treatment of bacterial pathogens, where numerous resistance mechanisms that counteract their function are becoming increasingly prevalent. Here, we utilize an unconventional anti-virulence screen of host-guest interacting macrocycles, and identify a water-soluble synthetic macrocycle, Pillar[5]arene, that is non-bactericidal/bacteriostatic and has a mechanism of action that involves binding to both homoserine lactones and lipopolysaccharides, key virulence factors in Gram-negative pathogens. Pillar[5]arene is active against Top Priority carbapenem- and third/fourth-generation cephalosporin-resistant Pseudomonas aeruginosa and Acinetobacter baumannii, suppressing toxins and biofilms and increasing the penetration and efficacy of standard-of-care antibiotics in combined administrations. The binding of homoserine lactones and lipopolysaccharides also sequesters their direct effects as toxins on eukaryotic membranes, neutralizing key tools that promote bacterial colonization and impede immune defenses, both in vitro and in vivo. Pillar[5]arene evades both existing antibiotic resistance mechanisms, as well as the build-up of rapid tolerance/resistance. The versatility of macrocyclic host-guest chemistry provides ample strategies for tailored targeting of virulence in a wide range of Gram-negative infectious diseases.

In a multi-disciplinary effort, we investigate the level of speckle that can be tolerated in a laser cinema projector based on a quality of experience experiment with movie clips shown to a test audience in a real-life movie theatre setting. We identify a speckle disturbance threshold by statistically analyzing the observers’ responses for different values of the amount of speckle, which was monitored using a well-defined speckle measurement method. The analysis shows that the speckle perception of a human observer is not only dependent on the objectively measured amount of speckle, but it is also strongly influenced by the image content. The speckle disturbance limit for movies turns out to be substantially larger than that for still images, and hence is easier to attain. ispartof: Scientific Reports vol:5 issue:1 ispartof: location:England status: published

Substituting carbon with silicon in organic molecules and materials has long been an attractive way to modify their electronic structure and properties. Silicon-doped graphene-based materials are known to exhibit exotic properties, yet conjugated organic materials with atomically precise Si substitution have remained difficult to prepare. Here we present the on-surface synthesis of one- and two-dimensional covalent organic frameworks whose backbones contain 1,4-disilabenzene (C4Si2) linkers. Silicon atoms were first deposited on a Au(111) surface, forming a AuSix film on annealing. The subsequent deposition and annealing of a bromo-substituted polyaromatic hydrocarbon precursor (triphenylene or pyrene) on this surface led to the formation of the C4Si2-bridged networks, which were characterized by a combination of high-resolution scanning tunnelling microscopy and photoelectron spectroscopy supported by density functional theory calculations. Each Si in a hexagonal C4Si2 ring was found to be covalently linked to one terminal Br atom. For the linear structure obtained with the pyrene-based precursor, the C4Si2 rings were converted into C4Si pentagonal siloles by further annealing.

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License., Reservoir computing is a novel bio-inspired computing method, capable of solving complex tasks in a computationally efficient way. It has recently been successfully implemented using delayed feedback systems, allowing to reduce the hardware complexity of brain-inspired computers drastically. In this approach, the pre-processing procedure relies on the definition of a temporal mask which serves as a scaled time-mutiplexing of the input. Originally, random masks had been chosen, motivated by the random connectivity in reservoirs. This random generation can sometimes fail. Moreover, for hardware implementations random generation is not ideal due to its complexity and the requirement for trial and error. We outline a procedure to reliably construct an optimal mask pattern in terms of multipurpose performance, derived from the concept of maximum length sequences. Not only does this ensure the creation of the shortest possible mask that leads to maximum variability in the reservoir states for the given reservoir, it also allows for an interpretation of the statistical significance of the provided training samples for the task at hand., This research was partially supported by the Belgian Science Policy Office, under grant IAP P7/35 Photonics@be, by FWO(Belgium), MICINN (Spain), Comunitat Autonoma de les Illes Balears, FEDER, and the European Commission under Projects TEC2012-36335 (TRIPHOP), Grups Competitius and EC FP7 Projects PHOCUS (Grant No. 240763).

We propose a class of tangled vortex structures, tied from non-Abelian topological vortices, which are immune against decaying through local reconnections and strand crossings that are allowed by the system. We refer to such structures as being topologically protected. We then turn our attention to topological vortices classified by the quaternion group $Q_8$ ($Q_8$-colored links), which are realizable in systems consisting either of the biaxial nematic or the cyclic phase of a spin-2 Bose--Einstein condensate, or of biaxial nematic liquid crystal, and prove the existence of topologically protected $Q_8$-colored links. Remarkably, the strongest invariant we construct, the $Q$-invariant of $Q_8$-colored links, can be used to classify $Q_8$-colored links up to allowed local surgeries on the vortex cores., 29 pages, 12 figures. Comments welcome!

Funding Information: We are grateful to Henri Godfrin, Ari Harju, Ville Havu, Andreas Huettel, Martti Puska, and Erkki Thuneberg for discussions, and Petri Tonteri from Densiq Ltd. (90620 Oulu, Finland) for providing us with the ultra-pure grafoil. We thank Miika Haataja for measuring the surface area of the grafoil sample and Qiang Zhang for participation in the optimization of the CNT process. Funding: This work was supported by Academy of Finland projects No. 314448 (BOLOSE), No. 312295 (CoE, Quantum Technology Finland), and No. 316572 (CNTstress). The research leading to these results has received funding from the European Union’s Horizon 2020 Research and Innovation Programme, under Grant Agreement No 824109 (EMP), under ERC Grant No. 670743 (QuDeT), and in part by Marie-Curie training network project (OMT, No. 722923). J.-P.K. is grateful for the financial support from Vilho, Yrjö and Kalle Väisälä Foundation of the Finnish Academy of Science and Letters. This research project utilized the Aalto University OtaNano/LTL infrastructure. | openaire: EC/H2020/670743/EU//QuDeT | openaire: EC/H2020/824109/EU//EMP | openaire: EC/H2020/722923/EU//OMT Low dimensional fermionic quantum systems are exceptionally interesting because they reveal distinctive physical phenomena, including among others, topologically protected excitations, edge states, frustration, and fractionalization. Our aim was to confine 3He on a suspended carbon nanotube to form 2-dimensional Fermi-system. Here we report our measurements of the mechanical resonance of the nanotube with adsorbed sub-monolayer down to 10 mK. At intermediate coverages we have observed the famous 1/3 commensurate solid. However, at larger monolayer densities we have observed a quantum phase transition from 1/3 solid to an unknown, soft, and mobile solid phase. We interpret this mobile solid phase as a bosonic commensurate crystal consisting of helium dimers with topologically-induced zero-point vacancies which are delocalized at low temperatures. We thus demonstrate that 3He on a nanotube merges both fermionic and bosonic phenomena, with a quantum phase transition between fermionic solid 1/3 phase and the observed bosonic dimer solid.

With modern scanning probe microscopes, it is possible to manipulate surface structures even at the atomic level. However, manipulation of nanoscale objects such as clusters is often more relevant and also more challenging due to the complicated interactions between the surface, cluster and apparatus. We demonstrate the manipulation of nanometer scale gold clusters on the NaCl(001) surface with a non-contact atomic force microscope, and show that the movement of clusters is in certain cases constrained to specific crystallographic directions. First principles calculations explain this kinetic anisotropy as the result of the cluster attaching to surface defects: cation vacancies allow the clusters to bond in such a way that they only move in one direction. Constraining the movement of clusters could be exploited in the construction of nanostructures or nanomechanical devices, and the manipulation signatures may also be used for identifying cluster-defect complexes.

Novel methods for information processing are highly desired in our information-driven society. Inspired by the brain's ability to process information, the recently introduced paradigm known as 'reservoir computing' shows that complex networks can efficiently perform computation. Here we introduce a novel architecture that reduces the usually required large number of elements to a single nonlinear node with delayed feedback. Through an electronic implementation, we experimentally and numerically demonstrate excellent performance in a speech recognition benchmark. Complementary numerical studies also show excellent performance for a time series prediction benchmark. These results prove that delay-dynamical systems, even in their simplest manifestation, can perform efficient information processing. This finding paves the way to feasible and resource-efficient technological implementations of reservoir computing., The paradigm of reservoir computing shows that, like the human brain, complex networks can perform efficient information processing. Here, a simple delay dynamical system is demonstrated that can efficiently perform computations capable of replacing a complex network in reservoir computing.

Funding Information: We acknowledge support from the FWF DACH project I3827-N36, COST action CA18234, the Academy of Finland through projects 316601 and 334532 and the doctoral colleges Solids4Fun W1243-N16 funded by the FWF and TU-D funded by TU Wien. Christoph Schattauer acknowledges support as a recipient of a DOC fellowship of the Austrian Academy of Sciences. Numerical calculations were performed on the Vienna Scientific Clusters VSC3 and VSC4. Funding Information: iPALM imaging was done in collaboration with the Advanced Imaging Center at Janelia Research Campus, a facility jointly supported by the Gordon and Betty Moore Foundation and the Howard Hughes Medical Institute. ChIA-Drop analysis was done by Minji Kim and Michał Denkiewicz. Molecular graphics and analyses performed with UCSF Chimera, developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, with support from NIH P41-GM103311. This work was carried out within „Three-dimensional Human Genome structure at the population scale: computational algorithm and experimental validation for lymphoblastoid cell lines of selected families from 1000 Genomes Project” project carried out within the TEAM programme of the Foundation for Polish Science co-financed by the European Union under the European Regional Development Fund, co-supported by Polish National Science Centre (2019/35/O/ST6/02484 and 2020/37/B/NZ2/03757) and the grant 1U54DK107967-01 “Nucleome Positioning System for Spatiotemporal Genome Organization and Regulation” within 4D Nucleome NIH program. The work was co-supported by the European Commission as Horizon 2020 Marie Skłodowska-Curie ITN Enhpathy grant “Molecular Basis of Human enhanceropathies”. DP was co-funded by Warsaw University of Technology within the Excellence Initiative: Research University (IDUB) programme; and POB Cybersecurity and data analysis of Warsaw University of Technology within the Excellence Initiative: Research University (IDUB) programme. Computations were performed thanks to the Laboratory of Bioinformatics and Computational Genomics, Faculty of Mathematics and Information Science, Warsaw University of Technology using Artificial Intelligence HPC platform financed by Polish Ministry of Science and Higher Education (decision no. 7054/IA/SP/2020 of 2020-08-28). Publisher Copyright: © 2022, The Author(s). We employ machine learning to derive tight-binding parametrizations for the electronic structure of defects. We test several machine learning methods that map the atomic and electronic structure of a defect onto a sparse tight-binding parameterization. Since Multi-layer perceptrons (i.e., feed-forward neural networks) perform best we adopt them for our further investigations. We demonstrate the accuracy of our parameterizations for a range of important electronic structure properties such as band structure, local density of states, transport and level spacing simulations for two common defects in single layer graphene. Our machine learning approach achieves results comparable to maximally localized Wannier functions (i.e., DFT accuracy) without prior knowledge about the electronic structure of the defects while also allowing for a reduced interaction range which substantially reduces calculation time. It is general and can be applied to a wide range of other materials, enabling accurate large-scale simulations of material properties in the presence of different defects.

Processes that lead to the critical-current suppression and change of impedance of a superconductor under the application of an external voltage is an active area of research, especially due to various possible technological applications. In particular, field-effect transistors and radiation detectors have been developed in the recent years, showing the potential for precision and sensitivity exceeding their normal-metal counterparts. In order to describe the phenomenon that leads to the critical-current suppression in metallic superconducting structures, a field-effect hypothesis has been formulated, stating that an electric field can penetrate the metallic superconductor and affect its characteristics. The existence of such an effect would imply the incompleteness of the underlying theory, and hence indicate an important gap in the general comprehension of superconductors. In addition to its theoretical value, a complete understanding of the phenomenon underneath the electric-field response of the superconductor is important in the light of the related technological applications. In this paper, we study the change of the characteristics of a superconductor implementing a coplanar-waveguide resonator as a tank circuit, by relating our measurements to the reactance and resistance of the material. Namely, we track the state of the superconductor at different voltages and resulting leakage currents of a nearby gate electrode which is not galvanically connected to the resonator. By comparing the effects of the leakage current and of a change in the temperature of the system, we conclude that the observed behaviour in the superconductor is [...], Comment: 10 pages, 4 figures

A curved image sensor on plastic foil has been developed for cone beam computed tomography (CBCT) X-ray imaging. The image sensor of about 6 × 8 cm2 size has been built on a thin polyimide foil with an indium gallium zinc oxide (IGZO) backplane and an organic photodetectors (OPD) frontplane. A flexible cesium iodide (CsI) scintillator has been attached to the optical sensor with 480 × 640 pixels of 126 µm size. Dark current density of the OPD was low with less than 10−7 mA/cm2 at −2 V, while an external quantum efficiency (EQE) of about 50% was reached in the visible wavelength range matched to the scintillator output. The image quality of the digital X-ray detector allowed for 3D reconstruction images of a bone phantom on a rotating stage with a lab setup. The curved detector with 32 cm curvature radius opens up the path for very compact CBCT gantries with largely reduced footprint.

Successful application of two-dimensional transition metal dichalcogenides in optoelectronic, catalytic, or sensing devices heavily relies on the materials’ quality, that is, the thickness uniformity, presence of grain boundaries, and the types and concentrations of point defects. Raman spectroscopy is a powerful and nondestructive tool to probe these factors but the interpretation of the spectra, especially the separation of different contributions, is not straightforward. Comparison to simulated spectra is beneficial, but for defective systems first-principles simulations are often computationally too expensive due to the large sizes of the systems involved. Here, we present a combined first-principles and empirical potential method for simulating Raman spectra of defective materials and apply it to monolayer MoS2 with random distributions of Mo and S vacancies. We study to what extent the types of vacancies can be distinguished and provide insight into the origin of different evolutions of Raman spectra upon increasing defect concentration. We apply to our simulated spectra the phonon confinement model used in previous experiments to assess defect concentrations, and show that the simplest form of the model is insufficient to fully capture peak shapes, but a good match is obtained when the type of phonon confinement and the full phonon dispersion relation are accounted for.

In microbial ecosystems, species not only compete for common resources but may also display mutualistic interactions as a result from metabolic cross-feeding. Such mutualism can lead to bistability. Depending on the initial population sizes, species will either survive or go extinct. Various phenomenological models have been suggested to describe bistability in mutualistic systems. However, these models do not account for interaction mediators such as nutrients. In contrast, nutrient-explicit models do not provide an intuitive understanding of what causes bistability. Here, we reduce a theoretical nutrient-explicit model of two mutualistic cross-feeders in a chemostat, uncovering an explicit relation to a growth model with an Allee effect. We show that the dilution rate in the chemostat leads to bistability by turning a weak Allee effect into a strong Allee effect. This happens as long as there is more production than consumption of cross-fed nutrients. Thanks to the explicit relationship of the reduced model with the underlying experimental parameters, these results allow to predict the biological conditions that sustain or prevent the survival of mutualistic species., SCOPUS: ar.j, info:eu-repo/semantics/published

Unitary Fourier transform lies at the core of the multitudinous computational and metrological algorithms. Here we show experimentally how the unitary Fourier transform-based phase estimation protocol, used namely in quantum metrology, can be translated into the classical linear optical framework. The developed setup made of beam splitters, mirrors and phase shifters demonstrates how the classical coherence, similarly to the quantum coherence, poses a resource for obtaining information about the measurable physical quantities. Our study opens route to the reliable implementation of the small-scale unitary algorithms on path-encoded qudits, thus establishing an easily accessible platform for unitary computation., Comment: 17 pages (main text: 9 pages, supplement: 8 pages), 7 figures (main text: 5 figures, supplement: 2 figures)

The integration and cooperation of mechanoreceptors, neurons and synapses in somatosensory systems enable humans to efficiently sense and process tactile information. Inspired by biological somatosensory systems, we report an optoelectronic spiking afferent nerve with neural coding, perceptual learning and memorizing capabilities to mimic tactile sensing and processing. Our system senses pressure by MXene-based sensors, converts pressure information to light pulses by coupling light-emitting diodes to analog-to-digital circuits, then integrates light pulses using a synaptic photomemristor. With neural coding, our spiking nerve is capable of not only detecting simultaneous pressure inputs, but also recognizing Morse code, braille, and object movement. Furthermore, with dimensionality-reduced feature extraction and learning, our system can recognize and memorize handwritten alphabets and words, providing a promising approach towards e-skin, neurorobotics and human-machine interaction technologies., Designing artificial somatosensory systems to efficiently emulate biological tactile information sensing, coding, and processing remains a challenge. Here, the authors demonstrate a tactile sensory system based on optoelectronic spiking afferent nerves with both coding and learning capabilities.

npj 2D materials and applications 6(1), 42 (2022). doi:10.1038/s41699-022-00318-4, Published by Nature Publishing Group, London

We draw a picture of physical systems that allows us to recognize what “time” is by requiring consistency with the way that time enters the fundamental laws of Physics. Elements of the picture are two non-interacting and yet entangled quantum systems, one of which acting as a clock. The setting is based on the Page and Wootters mechanism, with tools from large-N quantum approaches. Starting from an overall quantum description, we first take the classical limit of the clock only, and then of the clock and the evolving system altogether; we thus derive the Schrödinger equation in the first case, and the Hamilton equations of motion in the second. This work shows that there is not a “quantum time”, possibly opposed to a “classical” one; there is only one time, and it is a manifestation of entanglement., Discussions about the role of time in quantum mechanics are often detached from the corresponding classical limit. Here, the authors provide the Page and Wootters mechanism with a classical limit using the large-N approach based on generalized coherent states, without the need to introduce time measurements.

Generation of electric voltage in a conductor by applying a temperature gradient is a fundamental phenomenon called the Seebeck effect. This effect and its inverse is widely exploited in diverse applications ranging from thermoelectric power generators to temperature sensing. Recently, a possibility of thermoelectricity arising from the interplay of the non-local Cooper pair splitting and the elastic co-tunneling in the hybrid normal metal-superconductor-normal metal structures was predicted. Here, we report the observation of the non-local Seebeck effect in a graphene-based Cooper pair splitting device comprising two quantum dots connected to an aluminum superconductor and present a theoretical description of this phenomenon. The observed non-local Seebeck effect offers an efficient tool for producing entangled electrons., Thermoelectricity due to the interplay of the nonlocal Cooper pair splitting and the elastic co-tunneling in normal metal-superconductor-normal metal structure is predicted. Here, the authors observe the non-local Seebeck effect in a graphene-based Cooper pair splitting device.

Heavy-fermion systems represent one of the paradigmatic strongly correlated states of matter1–5. They have been used as a platform for investigating exotic behaviour ranging from quantum criticality and non-Fermi liquid behaviour to unconventional topological superconductivity4–12. The heavy-fermion phenomenon arises from the exchange interaction between localized magnetic moments and conduction electrons leading to Kondo lattice physics, and represents one of the long-standing open problems in quantum materials3. In a Kondo lattice, the exchange interaction gives rise to a band with heavy effective mass. This intriguing phenomenology has so far been realized only in compounds containing rare-earth elements with 4f or 5f electrons1,4,13,14. Here we realize a designer van der Waals heterostructure where artificial heavy fermions emerge from the Kondo coupling between a lattice of localized magnetic moments and itinerant electrons in a 1T/1H-TaS2 heterostructure. We study the heterostructure using scanning tunnelling microscopy and spectroscopy and show that depending on the stacking order of the monolayers, we can reveal either the localized magnetic moments and the associated Kondo effect, or the conduction electrons with a heavy-fermion hybridization gap. Our experiments realize an ultimately tunable platform for future experiments probing enhanced many-body correlations, dimensional tuning of quantum criticality and unconventional superconductivity in two-dimensional artificial heavy-fermion systems15–17. A study demonstrates the synthesis and characterization of a two-dimensional van der Waals heterostructure hosting artificial heavy fermions, providing a tunable platform for investigations of heavy-fermion physics.

Nonlinearity and topology are both linked to symmetries, but what happens when the two are combined is not a trivial question. In a nonlinear photonic higher-order topological insulator, solitons localize on the corners together with the topological modes. Non

A confined electronic system can host a wide variety of fascinating electronic, magnetic, valleytronic and photonic phenomena due to its reduced symmetry and quantum confinement effect. For the recently emerging one-dimensional van der Waals (1D vdW) materials with electrons confined in 1D sub-units, an enormous variety of intriguing physical properties and functionalities can be expected. Here, we demonstrate the coexistence of giant linear/nonlinear optical anisotropy and high emission yield in fibrous red phosphorus (FRP), an exotic 1D vdW semiconductor with quasi-flat bands and a sizeable bandgap in the visible spectral range. The degree of photoluminescence (third-order nonlinear) anisotropy can reach 90% (86%), comparable to the best performance achieved so far. Meanwhile, the photoluminescence (third-harmonic generation) intensity in 1D vdW FRP is strong, with quantum efficiency (third-order susceptibility) four (three) times larger than that in the most well-known 2D vdW materials (e.g., MoS2). The concurrent realization of large linear/nonlinear optical anisotropy and emission intensity in 1D vdW FRP paves the way towards transforming the landscape of technological innovations in photonics and optoelectronics., One-dimensional van der Waals (1D vdW) materials derive interesting behaviour from dimensional confinement. Here the authors study a 1D vdW semiconductor, fibrous red phosphorous, and observe exceptional optical properties of large optical anisotropy and high photoluminescence.

Vertical van der Waals (vdW) heterostructures of 2D crystals with defined interlayer twist are of interest for band-structure engineering via twist moiré superlattice potentials. To date, twist-heterostructures have been realized by micromechanical stacking. Direct synthesis is hindered by the tendency toward equilibrium stacking without interlayer twist. Here, we demonstrate that growing a 2D crystal with fixed azimuthal alignment to the substrate followed by transformation of this intermediate enables a potentially scalable synthesis of twisted heterostructures. Microscopy during growth of ultrathin orthorhombic SnS on trigonal SnS2 shows that vdW epitaxy yields azimuthal order even for non-isotypic 2D crystals. Excess sulfur drives a spontaneous transformation of the few-layer SnS to SnS2, whose orientation – rotated 30° against the underlying SnS2 crystal – is defined by the SnS intermediate rather than the substrate. Preferential nucleation of additional SnS on such twisted domains repeats the process, promising the realization of complex twisted stacks by bottom-up synthesis., Vertically stacked twisted layers of two-dimensional materials can trigger exciting fundamental physics. Here, authors report controlled growth of 30° twisted few-layer SnS2 over SnS2 via van der Waals epitaxy of an SnS intermediate and its transformation in the presence of excess sulfur.

The tight organization of major wood cell wall polymers limits the swellability, solubility and reactivity of cellulose fibers during the production of regenerated textile fibers, nanocellulose, bioethanol, and many other value-added products. However, the ultrastructural assembly of cellulose elementary fibrils (EF) and matrix materials in one of the outer layers, i.e. S1-2 transition layer of wood cell wall, is far from being understood. Here, single-axis electron tomography on ultrathin spruce sections was applied to observe the three-dimensional (3D) structure of the S1-2 layer. The nanoscale geometries of the EFs were further quantitatively modeled through mathematical fitting of the tomographic subvolumes by suitable parametric space curves. The results showed that crisscross, bundled and parallel EF organizations are all present in this layer; the former two exhibit a denser structure. Several quantitative measures such as distances and angles were obtained for the analyzed structures. The result obtained in this study suggests that the S1-2 transition layer differs in structure than the principal cell wall layers. The structural differences and its possible role in wood cell wall have been discussed. These results will enhance our understanding of the swellability, accessibility and solubility of woody biomass for its conversion into the aforementioned value-added products.

Symmetries of the physical world have guided formulation of fundamental laws, including relativistic quantum field theory and understanding of possible states of matter. Topological defects (TDs) often control the universal behavior of macroscopic quantum systems, while topology and broken symmetries determine allowed TDs. Taking advantage of the symmetry-breaking patterns in the phase diagram of nanoconfined superfluid $^3$He, we show that half-quantum vortices (HQVs) -- linear topological defects carrying half quantum of circulation -- survive transitions from the polar phase to other superfluid phases with polar distortion. In the polar-distorted A phase, HQV cores in 2D systems should harbor non-Abelian Majorana modes. In the polar-distorted B phase, HQVs form composite defects -- walls bounded by strings hypothesized decades ago in cosmology. Our experiments establish the superfluid phases of $^3$He in nanostructured confinement as a promising topological media for further investigations ranging from topological quantum computing to cosmology and grand unification scenarios., Comment: 17 pages, 11 figures

Funding Information: This research was supported by a JSPS Grant-in-aid for scientific research (KAKENHI, 15H04359, and 18H02385). Publisher Copyright: © 2021, The Author(s). Copyright: Copyright 2021 Elsevier B.V., All rights reserved. After several months of "lockdown" as the sole answer to the COVID-19 pandemic, balancing the re-opening of society against the implementation of non-pharmaceutical measures needed for minimizing interpersonal contacts has become important. Here, we present a stochastic model that examines this problem. In our model, people are allowed to move between discrete positions on a one-dimensional grid with viral infection possible when two people are collocated at the same site. Our model features three sets of adjustable parameters, which characterize (i) viral transmission, (ii) viral detection, and (iii) degree of personal mobility, and as such, it is able to provide a qualitative assessment of the potential for second-wave infection outbreaks based on the timing, extent, and pattern of the lockdown relaxation strategies. Our results suggest that a full lockdown will yield the lowest number of infections (as anticipated) but we also found that when personal mobility exceeded a critical level, infections increased, quickly reaching a plateau that depended solely on the population density. Confinement was not effective if not accompanied by a detection/quarantine capacity surpassing 40% of the symptomatic patients. Finally, taking action to ensure a viral transmission probability of less than 0.4, which, in real life, may mean actions such as social distancing or mask-wearing, could be as effective as a soft lockdown.

The ability to propel against flows, i.e., to perform positive rheotaxis, can provide exciting opportunities for applications in targeted therapeutics and non-invasive surgery. To date, no biocompatible technologies exist for navigating microparticles upstream when they are in a background fluid flow. Inspired by many naturally occurring microswimmers such as bacteria, spermatozoa, and plankton that utilize the non-slip boundary conditions of the wall to exhibit upstream propulsion, here, we report on the design and characterization of self-assembled microswarms that can execute upstream motility in a combination of external acoustic and magnetic fields. Both acoustic and magnetic fields are safe to humans, non-invasive, can penetrate deeply into the human body, and are well-developed in clinical settings. The combination of both fields can overcome the limitations encountered by single actuation methods. The design criteria of the acoustically-induced reaction force of the microswarms, which is needed to perform rolling-type motion, are discussed. We show quantitative agreement between experimental data and our model that captures the rolling behaviour. The upstream capability provides a design strategy for delivering small drug molecules to hard-to-reach sites and represents a fundamental step toward the realization of micro- and nanosystem-navigation against the blood flow., 22 pages

Radiation sensors based on the heating effect of absorbed radiation are typically simple to operate and flexible in terms of input frequency, so they are widely used in gas detection 1, security 2, terahertz imaging 3, astrophysical observations 4 and medical applications 5. Several important applications are currently emerging from quantum technology and especially from electrical circuits that behave quantum mechanically, that is, circuit quantum electrodynamics 6. This field has given rise to single-photon microwave detectors 7–9 and a quantum computer that is superior to classical supercomputers for certain tasks 10. Thermal sensors hold potential for enhancing such devices because they do not add quantum noise and they are smaller, simpler and consume about six orders of magnitude less power than the frequently used travelling-wave parametric amplifiers 11. However, despite great progress in the speed 12 and noise levels 13 of thermal sensors, no bolometer has previously met the threshold for circuit quantum electrodynamics, which lies at a time constant of a few hundred nanoseconds and a simultaneous energy resolution of the order of 10h gigahertz (where h is the Planck constant). Here we experimentally demonstrate a bolometer that operates at this threshold, with a noise-equivalent power of 30 zeptowatts per square-root hertz, comparable to the lowest value reported so far 13, at a thermal time constant two orders of magnitude shorter, at 500 nanoseconds. Both of these values are measured directly on the same device, giving an accurate estimation of 30h gigahertz for the calorimetric energy resolution. These improvements stem from the use of a graphene monolayer with extremely low specific heat 14 as the active material. The minimum observed time constant of 200 nanoseconds is well below the dephasing times of roughly 100 microseconds reported for superconducting qubits 15 and matches the timescales of currently used readout schemes 16,17, thus enabling circuit quantum electrodynamics applications for bolometers.

openaire: EC/H2020/725513/EU//SuperRepel Superhydrophobicity is a remarkable surface property found in nature and mimicked in many engineering applications, including anti-wetting, anti-fogging, and anti-fouling coatings. As synthetic superhydrophobic coatings approach the extreme non-wetting limit, quantification of their slipperiness becomes increasingly challenging: although contact angle goniometry remains widely used as the gold standard method, it has proven insufficient. Here, micropipette force sensors are used to directly measure the friction force of water droplets moving on super-slippery superhydrophobic surfaces that cannot be quantified with contact angle goniometry. Superhydrophobic etched silicon surfaces with tunable slipperiness are investigated as model samples. Micropipette force sensors render up to three orders of magnitude better force sensitivity than using the indirect contact angle goniometry approach. We directly measure a friction force as low as 7 ± 4 nN for a millimetric water droplet moving on the most slippery surface. Finally, we combine micropipette force sensors with particle image velocimetry and reveal purely rolling water droplets on superhydrophobic surfaces.

Terminating the tip of an atomic force microscope with a CO molecule allows data to be acquired with a well-known and inert apex. Previous studies have shown conflicting results regarding the electrostatic interaction, indicating in some cases that the negative charge at the apex of the CO dominates, whereas in other cases the positive charge at the end of the metal tip dominates. To clarify this, we investigated $$\hbox {CaF}_{2}$$ CaF 2 (111). $$\hbox {CaF}_{2}$$ CaF 2 is an ionic crystal and the (111) surface does not possess charge inversion symmetry. Far from the surface, the interaction is dominated by electrostatics via the negative charge at the apex. Closer to the surface, Pauli repulsion and CO bending dominate, which leads to an unexpected appearance of the complex 3-atom unit cell. We compare simulated data in which the electrostatics are modeled by point particles versus a charge density calculated by DFT. We also compare modeling Pauli repulsion via individual Lennard–Jones potentials versus a total charge density overlap. In doing so, we determine forcefield parameters useful for future investigations of biochemical processes.

Ever since its discovery around a decade ago, all-optical magnetization switching (AOS) using femtosecond laser pulses has shown potential for future data storage and logic devices. In particular, single pulse helicity independent AOS in certain ferrimagnetic alloys and multilayers is highly efficient and ultrafast. However, in most cases it is a toggle mechanism, which is not desirable for applications. Here we experimentally demonstrate conversion from toggle switching to a deterministic mechanism by biasing AOS in a Co/Gd bilayer with a spin polarized current which is optically generated in an adjacent ferromagnetic reference layer. We show deterministic writing of an ‘up’ and ‘down’ state using a sequence of one or two pulses, respectively, and demonstrate the non-local origin by varying the magnitude of the generated spin current. Our demonstration of deterministic magnetization writing could provide an essential step towards the implementation of future optically addressable spintronic memory devices., Some magnetic materials can switch magnetization via a single laser pulse. However, while very fast, the mechanism is not deterministic. Here, the authors demonstrate a deterministic method of writing opposite magnetization states optically with a sequence of one or two laser pulses.

A particular class of focused, pulsed light beams can propagate self-similarly in free space at a fixed group velocity. Now, scientists present a law of refraction that determines how the group velocity of these beams changes as they refract at an interface between two materials.

There has been enormous recent interest in heterostructures of two-dimensional van der Waals materials. Integrating materials with different quantum ground states in vertical heterostructures is predicted to lead to novel electronic properties that are not found in the constituent layers. Here, we present direct synthesis of a superconductor-magnet hybrid heterostructure by combining superconducting niobium diselenide (NbSe) with the monolayer vanadium diselenide (VSe). Molecular-beam epitaxy growth in ultra-high vacuum yields clean and atomically sharp interfaces. Combining different characterization techniques and density-functional theory calculations, we investigate the electronic and magnetic properties of VSe on NbSe. Low temperature scanning tunneling microscopy measurements show an absence of the typical charge density wave on VSe and demonstrate a reduction of the superconducting gap of NbSe on the VSe layer. This suggests magnetization of the VSe sheet, at least on the local scale. Our work demonstrates superconducting-magnetic hybrid materials with potential applications in future electronics devices., This research made use of the Aalto Nanomicroscopy Center (Aalto NMC) facilities and was supported by the European Research Council (ERC-2017-AdG no. 788185 “Artificial Designer Materials”) and Academy of Finland (Academy professor funding no. 318995 and 320555, Academy postdoctoral researcher no. 309975, and Academy research fellow no. 311058). Our DFT calculations were performed using computer resources within the Aalto University School of Science “Science-IT” project and the Finnish CSC-IT Center for Science. M.M.U. acknowledges support by the Spanish MINECO under grant no. MAT2017-82074-ERC and by the ERC Starting grant LINKSPM (Grant 758558).

Saturn’s moon Titan has a methane cycle with clouds, rain, rivers, lakes, and seas; it is the only world known to presently have a volatile cycle akin to Earth’s tropospheric water cycle. Anomalously specular radar reflections (ASRR) from Titan’s tropical region were observed with the Arecibo Observatory (AO) and Green Bank Telescope (GBT) and interpreted as evidence for liquid surfaces. The Cassini spacecraft discovered lakes/seas on Titan, however, it did not observe lakes/seas at the AO/GBT anomalously specular locations. A satisfactory explanation for the ASRR has been elusive for more than a decade. Here we show that the ASRR originate from one terrain unit, likely paleolakes/paleoseas. Titan observations provide ground-truth in the search for oceans on exoearths and an important lesson is that identifying liquid surfaces by specular reflections requires a stringent definition of specular; we propose a definition for this purpose., Anomalously specular radar reflections (ASRR) from Titan’s tropical region were interpreted earlier as evidence for liquid surfaces, but the Cassini spacecraft did not observe lakes/seas at the anomalously specular locations. Here, the authors show that ASRR originate from one terrain unit, likely paleolakes/paleoseas.

The ability of superhydrophobic surfaces to stay dry, self-clean and avoid biofouling is attractive for applications in biotechnology, medicine and heat transfer1–10. Water droplets that contact these surfaces must have large apparent contact angles (greater than 150 degrees) and small roll-off angles (less than 10 degrees). This can be realized for surfaces that have low-surface-energy chemistry and micro- or nanoscale surface roughness, minimizing contact between the liquid and the solid surface11–17. However, rough surfaces—for which only a small fraction of the overall area is in contact with the liquid—experience high local pressures under mechanical load, making them fragile and highly susceptible to abrasion18. Additionally, abrasion exposes underlying materials and may change the local nature of the surface from hydrophobic to hydrophilic19, resulting in the pinning of water droplets to the surface. It has therefore been assumed that mechanical robustness and water repellency are mutually exclusive surface properties. Here we show that robust superhydrophobicity can be realized by structuring surfaces at two different length scales, with a nanostructure design to provide water repellency and a microstructure design to provide durability. The microstructure is an interconnected surface frame containing ‘pockets’ that house highly water-repellent and mechanically fragile nanostructures. This surface frame acts as ‘armour’, preventing the removal of the nanostructures by abradants that are larger than the frame size. We apply this strategy to various substrates—including silicon, ceramic, metal and transparent glass—and show that the water repellency of the resulting superhydrophobic surfaces is preserved even after abrasion by sandpaper and by a sharp steel blade. We suggest that this transparent, mechanically robust, self-cleaning glass could help to negate the dust-contamination issue that leads to a loss of efficiency in solar cells. Our design strategy could also guide the development of other materials that need to retain effective self-cleaning, anti-fouling or heat-transfer abilities in harsh operating environments. Water-repellent nanostructures are housed within an interconnected microstructure frame to yield mechanically robust superhydrophobic surfaces.

Banerdt, William B. et al., NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude M = 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately M = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding M = 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

Here, we follow the stable propagation of a roughening crack using simultaneously Digital Image Correlation and Infra-Red imaging. In a quasi-two-dimensional paper sample, the crack tip and ahead of that the fracture process zone follow the slowly, diffusively moving “hot spot” ahead of the tip. This also holds when the crack starts to roughen during propagation. The well-established intermittency of the crack advancement and the roughening of the crack in paper are thus subject to the dissipation and decohesion in the hot spot zone. They are therefore not only a result of the depinning of the crack in a heterogeneous material.

Compared to the limited absorption cross-section of conventional photoactive TiO2 nanoparticles (NPs), plasmonic metallic nanoparticles can efficiently convert photons from an extended spectrum range into energetic carriers because of the localized surface plasmon resonance (LSPR). Using these metal oxide semiconductors as shells for plasmonic nanoparticles (PNPs) that absorb visible light could extend their applications. The photophysics of such systems is performed using transient absorption measurements and steady extinction simulations and shows that the plasmonic energy transfer from the AgNWs core to the TiO2 shell results from a hot carrier injection process. Lifetimes obtained from photobleaching decay dynamics suggest that (i) the presence of gold nanoparticles (AuNPs) in AgNWs@TiO2@AuNPs systems can further promote the hot carrier transfer process via plasmonic coupling effects and (ii) the carrier dynamics is greatly affected by the shell thickness of TiO2. This result points out a definite direction to design appropriate nanostructures with tunable charge transfer processes toward photo-induced energy conversion applications.

Site-selective functionalization of only one of two identical chemical groups within one molecule is highly challenging, which hinders the production of complex organic macromolecules. Here we demonstrate that adsorption of 4,4″-diamino-p-terphenyl on a metal surface leads to a dissymmetric binding affinity. With low temperature atomic force microscopy, using CO-tip functionalization, we reveal the asymmetric adsorption geometries of 4,4″-diamino-p-terphenyl on Cu(111), while on Au(111) the symmetry is retained. This symmetry breaking on Cu(111) is caused by a lattice mismatch and interactions with the subsurface atomic layer. The dissymmetry results in a change of the binding affinity of one of the amine groups, leading to a non-stationary behavior under the influence of the scanning tip. Finally, we exploit this dissymmetric binding affinity for on-surface self-assembly with 4,4″-diamino-p-terphenyl for side-preferential attachment of 2-triphenylenecarbaldehyde. Our findings provide a new route towards surface-induced dissymmetric activation of a symmetric compound., In a symmetric molecule with identical functional groups, selective activation of only one site is challenging. Here, the authors show that 4,4″-diamino-p-terphenyl adsorbs asymmetrically to a metal surface, leading to a change in binding affinity of one of its amine groups.

Engineering, controlling, and simulating quantum dynamics is a strenuous task. However, these techniques are crucial to develop quantum technologies, preserve quantum properties, and engineer decoherence. Earlier results have demonstrated reservoir engineering, construction of a quantum simulator for Markovian open systems, and controlled transition from Markovian to non-Markovian regime. Dephasing is an ubiquitous mechanism to degrade the performance of quantum computers. However, a fully controllable all-purpose quantum simulator for generic dephasing is still missing. Here we demonstrate full experimental control of dephasing allowing us to implement arbitrary decoherence dynamics of a qubit. As examples, we use a photon to simulate the dynamics of a qubit coupled to an Ising chain in a transverse field and also demonstrate a simulation of non-positive dynamical map. Our platform opens the possibility to simulate dephasing of any physical system and study fundamental questions on open quantum systems., V2: Added some text and new figure

We report development and microwave characterization of rf SQUID (Superconducting QUantum Interference Device) qubits, consisting of an aluminium-based Josephson junction embedded in a superconducting loop patterned from a thin film of TiN with high kinetic inductance. Here we demonstrate that the systems can offer small physical size, high anharmonicity, and small scatter of device parameters. The hybrid devices can be utilized as tools to shed further light onto the origin of film dissipation and decoherence in phase-slip nanowire qubits, patterned entirely from disordered superconducting films., Comment: 5 pages, 4 figures

We report the use of black silicon (bSi) as a growth platform for III–V nanowires (NWs), which enables low reflectance over a broad wavelength range as well as fabrication of optoelectronic devices by metalorganic vapor phase epitaxy. In addition, a new isolated growth regime is reported for self-catalyzed InAs NWs at record-low temperatures of 280 °C–365 °C, where consistently rectangular [-211]-oriented NWs are obtained. The bSi substrate is shown to support the growth of additionally GaAs and InP NWs, as well as heterostructured NWs. As seed particles, both ex-situ deposited Au nanoparticles and in-situ deposited In droplets are shown feasible. Particularly the InAs NWs with low band gap energy are used to extend low-reflectivity wavelength region into infrared, where the bSi alone remains transparent. Finally, a fabricated prototype device confirms the potential of III–V NWs combined with bSi for optoelectronic devices. Our results highlight the promise of III–V NWs on bSi for enhancing optoelectronic device performance on the low-cost Si substrates, and we believe that the new low-temperature NW growth regime advances the understanding and capabilities of NW growth.

We present a numerical study of the correlations in the occurrence times of consecutive crackling noise events in the nonequilibrium zero-temperature Random Field Ising model in three dimensions. The critical behavior of the system is portrayed by the intermittent bursts of activity known as avalanches with scale-invariant properties which are power-law distributed. Our findings, based on the scaling analysis and collapse of data collected in extensive simulations show that the observed correlations emerge upon applying a finite threshold to the pertaining signals when defining events of interest. Such events are called subavalanches and are obtained by separation of original avalanches in the thresholding process. The correlations are evidenced by power law distributed waiting times and are present in the system even when the original avalanche triggerings are described by a random uncorrelated process.