Pub Date : 2024-07-15DOI: 10.1038/s41567-024-02537-6
Andrei Stefancu, Naomi J. Halas, Peter Nordlander, Emiliano Cortes
The recent rise of plasmonic materials for solar-to-chemical energy conversion places a focus on the mechanisms associated with charge and energy flow at the metal–molecule interface. Understanding the connection between these effects and their roles in the plasmonic excitations of adsorbed molecules has been challenging. In this Review, we strive to provide a general framework—based on the concept of electron scattering—that encompasses the most important effects at the plasmonic metal–molecule interface. First we use the model of adsorbate-induced surface resistivity to understand the chemical specificity of the electron scattering process. We then analyse two of the most prominent effects in plasmonics through the lens of the electron scattering model: chemical interface damping and the chemical model of surface-enhanced Raman scattering. We show how most metal–adsorbate charge- or energy-transfer interactions can be mapped into two major classes—electron scattering through molecular resonances and direct non-resonant electron scattering. Plasmonic excitations can enhance the interaction between a metal and molecules adsorbed onto its surface. This Review summarizes the different effects involved in this process and places them into a framework based on electron scattering.
{"title":"Electronic excitations at the plasmon–molecule interface","authors":"Andrei Stefancu, Naomi J. Halas, Peter Nordlander, Emiliano Cortes","doi":"10.1038/s41567-024-02537-6","DOIUrl":"10.1038/s41567-024-02537-6","url":null,"abstract":"The recent rise of plasmonic materials for solar-to-chemical energy conversion places a focus on the mechanisms associated with charge and energy flow at the metal–molecule interface. Understanding the connection between these effects and their roles in the plasmonic excitations of adsorbed molecules has been challenging. In this Review, we strive to provide a general framework—based on the concept of electron scattering—that encompasses the most important effects at the plasmonic metal–molecule interface. First we use the model of adsorbate-induced surface resistivity to understand the chemical specificity of the electron scattering process. We then analyse two of the most prominent effects in plasmonics through the lens of the electron scattering model: chemical interface damping and the chemical model of surface-enhanced Raman scattering. We show how most metal–adsorbate charge- or energy-transfer interactions can be mapped into two major classes—electron scattering through molecular resonances and direct non-resonant electron scattering. Plasmonic excitations can enhance the interaction between a metal and molecules adsorbed onto its surface. This Review summarizes the different effects involved in this process and places them into a framework based on electron scattering.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 7","pages":"1065-1077"},"PeriodicalIF":17.6,"publicationDate":"2024-07-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141618358","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-11DOI: 10.1038/s41567-024-02579-w
Philipp Stammer
High harmonic generation has long been successfully described using the semi-classical three-step model. However, recent progress has introduced a quantum optical formulation, exposing the limitations of the semi-classical picture.
{"title":"On the limitations of the semi-classical picture in high harmonic generation","authors":"Philipp Stammer","doi":"10.1038/s41567-024-02579-w","DOIUrl":"10.1038/s41567-024-02579-w","url":null,"abstract":"High harmonic generation has long been successfully described using the semi-classical three-step model. However, recent progress has introduced a quantum optical formulation, exposing the limitations of the semi-classical picture.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 7","pages":"1040-1042"},"PeriodicalIF":17.6,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141584532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-10DOI: 10.1038/s41567-024-02575-0
Jing Wang, Zhaochen Liu
Inducing superconductivity in quantum anomalous Hall insulators is crucial to realize topological superconductors. Now a study shows superconducting correlations in the quantum anomalous Hall state, which can convert electrons on its one-way path into holes.
{"title":"A way to cross the Andreev bridge","authors":"Jing Wang, Zhaochen Liu","doi":"10.1038/s41567-024-02575-0","DOIUrl":"10.1038/s41567-024-02575-0","url":null,"abstract":"Inducing superconductivity in quantum anomalous Hall insulators is crucial to realize topological superconductors. Now a study shows superconducting correlations in the quantum anomalous Hall state, which can convert electrons on its one-way path into holes.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1525-1526"},"PeriodicalIF":17.6,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141566296","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-10DOI: 10.1038/s41567-024-02574-1
Anjana Uday, Gertjan Lippertz, Kristof Moors, Henry F. Legg, Rikkie Joris, Andrea Bliesener, Lino M. C. Pereira, A. A. Taskin, Yoichi Ando
Thin films of ferromagnetic topological insulator materials can host the quantum anomalous Hall effect without the need for an external magnetic field. Inducing Cooper pairing in such a material is a promising way to realize topological superconductivity with the associated chiral Majorana edge states. However, finding evidence of the superconducting proximity effect in such a state has remained a considerable challenge due to inherent experimental difficulties. Here we demonstrate crossed Andreev reflection across a narrow superconducting Nb electrode that is in contact with the chiral edge state of a quantum anomalous Hall insulator. In the crossed Andreev reflection process, an electron injected from one terminal is reflected out as a hole at the other terminal to form a Cooper pair in the superconductor. This is a compelling signature of induced superconducting pair correlation in the chiral edge state. The characteristic length of the crossed Andreev reflection process is found to be much longer than the superconducting coherence length in Nb, which suggests that the crossed Andreev reflection is, indeed, mediated by superconductivity induced on the quantum anomalous Hall insulator surface. Our results will invite future studies of topological superconductivity and Majorana physics, as well as for the search for non-abelian zero modes. The superconducting proximity effect has not been experimentally demonstrated in a quantum anomalous Hall insulator. Now this effect is observed in the chiral edge state of a ferromagnetic topological insulator.
{"title":"Induced superconducting correlations in a quantum anomalous Hall insulator","authors":"Anjana Uday, Gertjan Lippertz, Kristof Moors, Henry F. Legg, Rikkie Joris, Andrea Bliesener, Lino M. C. Pereira, A. A. Taskin, Yoichi Ando","doi":"10.1038/s41567-024-02574-1","DOIUrl":"10.1038/s41567-024-02574-1","url":null,"abstract":"Thin films of ferromagnetic topological insulator materials can host the quantum anomalous Hall effect without the need for an external magnetic field. Inducing Cooper pairing in such a material is a promising way to realize topological superconductivity with the associated chiral Majorana edge states. However, finding evidence of the superconducting proximity effect in such a state has remained a considerable challenge due to inherent experimental difficulties. Here we demonstrate crossed Andreev reflection across a narrow superconducting Nb electrode that is in contact with the chiral edge state of a quantum anomalous Hall insulator. In the crossed Andreev reflection process, an electron injected from one terminal is reflected out as a hole at the other terminal to form a Cooper pair in the superconductor. This is a compelling signature of induced superconducting pair correlation in the chiral edge state. The characteristic length of the crossed Andreev reflection process is found to be much longer than the superconducting coherence length in Nb, which suggests that the crossed Andreev reflection is, indeed, mediated by superconductivity induced on the quantum anomalous Hall insulator surface. Our results will invite future studies of topological superconductivity and Majorana physics, as well as for the search for non-abelian zero modes. The superconducting proximity effect has not been experimentally demonstrated in a quantum anomalous Hall insulator. Now this effect is observed in the chiral edge state of a ferromagnetic topological insulator.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 10","pages":"1589-1595"},"PeriodicalIF":17.6,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41567-024-02574-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141566295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-09DOI: 10.1038/s41567-024-02567-0
An improved optimization algorithm enables the training of large-scale neural quantum states in which the enormous number of neuron connections capture the intricate complexity of quantum many-body wavefunctions. This advance leads to unprecedented accuracy in paradigmatic quantum models, opening up new avenues for simulating and understanding complex quantum phenomena.
{"title":"Efficient optimization of deep neural quantum states","authors":"","doi":"10.1038/s41567-024-02567-0","DOIUrl":"10.1038/s41567-024-02567-0","url":null,"abstract":"An improved optimization algorithm enables the training of large-scale neural quantum states in which the enormous number of neuron connections capture the intricate complexity of quantum many-body wavefunctions. This advance leads to unprecedented accuracy in paradigmatic quantum models, opening up new avenues for simulating and understanding complex quantum phenomena.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1381-1382"},"PeriodicalIF":17.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141561347","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-09DOI: 10.1038/s41567-024-02531-y
Peter L. McMahon
Nonlinearity is crucial for sophisticated tasks in machine learning but is often difficult to engineer outside of electronics. By encoding the inputs in parameters of the system, linear systems can realize efficiently trainable nonlinear computations.
{"title":"Nonlinear computation with linear systems","authors":"Peter L. McMahon","doi":"10.1038/s41567-024-02531-y","DOIUrl":"10.1038/s41567-024-02531-y","url":null,"abstract":"Nonlinearity is crucial for sophisticated tasks in machine learning but is often difficult to engineer outside of electronics. By encoding the inputs in parameters of the system, linear systems can realize efficiently trainable nonlinear computations.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1365-1366"},"PeriodicalIF":17.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141561507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-09DOI: 10.1038/s41567-024-02534-9
Clara C. Wanjura, Florian Marquardt
The increasing size of neural networks for deep learning applications and their energy consumption create a need for alternative neuromorphic approaches, for example, using optics. Current proposals and implementations rely on physical nonlinearities or optoelectronic conversion to realize the required nonlinear activation function. However, there are considerable challenges with these approaches related to power levels, control, energy efficiency and delays. Here we present a scheme for a neuromorphic system that relies on linear wave scattering and yet achieves nonlinear processing with high expressivity. The key idea is to encode the input in physical parameters that affect the scattering processes. Moreover, we show that gradients needed for training can be directly measured in scattering experiments. We propose an implementation using integrated photonics based on racetrack resonators, which achieves high connectivity with a minimal number of waveguide crossings. Our work introduces an easily implementable approach to neuromorphic computing that can be widely applied in existing state-of-the-art scalable platforms, such as optics, microwave and electrical circuits. As the energy consumption of neural networks continues to grow, different approaches to deep learning are needed. A neuromorphic method offering nonlinear computation based on linear wave scattering can be implemented using integrated photonics.
{"title":"Fully nonlinear neuromorphic computing with linear wave scattering","authors":"Clara C. Wanjura, Florian Marquardt","doi":"10.1038/s41567-024-02534-9","DOIUrl":"10.1038/s41567-024-02534-9","url":null,"abstract":"The increasing size of neural networks for deep learning applications and their energy consumption create a need for alternative neuromorphic approaches, for example, using optics. Current proposals and implementations rely on physical nonlinearities or optoelectronic conversion to realize the required nonlinear activation function. However, there are considerable challenges with these approaches related to power levels, control, energy efficiency and delays. Here we present a scheme for a neuromorphic system that relies on linear wave scattering and yet achieves nonlinear processing with high expressivity. The key idea is to encode the input in physical parameters that affect the scattering processes. Moreover, we show that gradients needed for training can be directly measured in scattering experiments. We propose an implementation using integrated photonics based on racetrack resonators, which achieves high connectivity with a minimal number of waveguide crossings. Our work introduces an easily implementable approach to neuromorphic computing that can be widely applied in existing state-of-the-art scalable platforms, such as optics, microwave and electrical circuits. As the energy consumption of neural networks continues to grow, different approaches to deep learning are needed. A neuromorphic method offering nonlinear computation based on linear wave scattering can be implemented using integrated photonics.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1434-1440"},"PeriodicalIF":17.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41567-024-02534-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141561348","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-09DOI: 10.1038/s41567-024-02572-3
Aawaz R. Pokhrel, Gabi Steinbach, Adam Krueger, Thomas C. Day, Julianne Tijani, Pablo Bravo, Siu Lung Ng, Brian K. Hammer, Peter J. Yunker
Bacteria often attach to surfaces and grow densely packed communities called biofilms. As biofilms grow, they expand across the surface, increasing their surface area and access to nutrients. Thus, the overall growth rate of a biofilm is directly dependent on its range expansion rate. A direct trade-off between horizontal and vertical growth impacts the range expansion rate and, crucially, the overall biofilm growth rate. The biophysical connection between horizontal and vertical growth remains poorly understood, in large part due to the difficulty in resolving the biofilm shape with sufficient spatial and temporal resolutions from small length scales to macroscopic sizes. Here we show that the horizontal expansion rate of bacterial colonies is strongly coupled to vertical expansion via the contact angle at the biofilm edge. Using white light interferometry, we measure the three-dimensional surface morphology of growing colonies, and find that small colonies are well described as spherical caps. At later times, nutrient diffusion and uptake prevent the tall colony centre from growing exponentially. We further show that a simple model connecting vertical and horizontal growth dynamics can reproduce the observed phenomena, suggesting that the spherical cap shape emerges due to the biophysical consequences of diffusion-limited growth. The growth of a biofilm—a bacterial colony attached to a surface—is governed by a trade-off between horizontal and vertical expansion. Now, it is shown that this process significantly depends on the contact angle at the biofilm’s edge.
{"title":"The biophysical basis of bacterial colony growth","authors":"Aawaz R. Pokhrel, Gabi Steinbach, Adam Krueger, Thomas C. Day, Julianne Tijani, Pablo Bravo, Siu Lung Ng, Brian K. Hammer, Peter J. Yunker","doi":"10.1038/s41567-024-02572-3","DOIUrl":"10.1038/s41567-024-02572-3","url":null,"abstract":"Bacteria often attach to surfaces and grow densely packed communities called biofilms. As biofilms grow, they expand across the surface, increasing their surface area and access to nutrients. Thus, the overall growth rate of a biofilm is directly dependent on its range expansion rate. A direct trade-off between horizontal and vertical growth impacts the range expansion rate and, crucially, the overall biofilm growth rate. The biophysical connection between horizontal and vertical growth remains poorly understood, in large part due to the difficulty in resolving the biofilm shape with sufficient spatial and temporal resolutions from small length scales to macroscopic sizes. Here we show that the horizontal expansion rate of bacterial colonies is strongly coupled to vertical expansion via the contact angle at the biofilm edge. Using white light interferometry, we measure the three-dimensional surface morphology of growing colonies, and find that small colonies are well described as spherical caps. At later times, nutrient diffusion and uptake prevent the tall colony centre from growing exponentially. We further show that a simple model connecting vertical and horizontal growth dynamics can reproduce the observed phenomena, suggesting that the spherical cap shape emerges due to the biophysical consequences of diffusion-limited growth. The growth of a biofilm—a bacterial colony attached to a surface—is governed by a trade-off between horizontal and vertical expansion. Now, it is shown that this process significantly depends on the contact angle at the biofilm’s edge.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1509-1517"},"PeriodicalIF":17.6,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141561231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-08DOI: 10.1038/s41567-024-02540-x
Suraj Shankar, L. Mahadevan
Muscle is a complex, hierarchically organized, soft contractile engine. To understand the limits on the rate of contraction and muscle energetics, we construct a coarse-grained multiscale model that describes muscle as an active sponge. Our analysis of existing experiments across species and muscle types highlights the importance of spatially heterogeneous strains and local volumetric deformations. Our minimal theoretical model shows how contractions induce intracellular fluid flow and power active hydraulic oscillations, yielding the limits of ultrafast muscular contractions. We further demonstrate that the viscoelastic response of muscle is naturally non-reciprocal—or odd—owing to its active and anisotropic nature. This enables an alternate mode of muscular power generation from periodic cycles in spatial strain alone, contrasting with previous descriptions based on temporal cycles. Our work suggests a revised view of muscle dynamics that emphasizes the multiscale spatiotemporal origins of soft hydraulic power, with potential implications for physiology, biomechanics and locomotion. A multiscale model of muscle as a fluid-filled sponge suggests that hydraulics limits rapid contractions and that the mechanical response of muscle is non-reciprocal.
{"title":"Active hydraulics and odd elasticity of muscle fibres","authors":"Suraj Shankar, L. Mahadevan","doi":"10.1038/s41567-024-02540-x","DOIUrl":"10.1038/s41567-024-02540-x","url":null,"abstract":"Muscle is a complex, hierarchically organized, soft contractile engine. To understand the limits on the rate of contraction and muscle energetics, we construct a coarse-grained multiscale model that describes muscle as an active sponge. Our analysis of existing experiments across species and muscle types highlights the importance of spatially heterogeneous strains and local volumetric deformations. Our minimal theoretical model shows how contractions induce intracellular fluid flow and power active hydraulic oscillations, yielding the limits of ultrafast muscular contractions. We further demonstrate that the viscoelastic response of muscle is naturally non-reciprocal—or odd—owing to its active and anisotropic nature. This enables an alternate mode of muscular power generation from periodic cycles in spatial strain alone, contrasting with previous descriptions based on temporal cycles. Our work suggests a revised view of muscle dynamics that emphasizes the multiscale spatiotemporal origins of soft hydraulic power, with potential implications for physiology, biomechanics and locomotion. A multiscale model of muscle as a fluid-filled sponge suggests that hydraulics limits rapid contractions and that the mechanical response of muscle is non-reciprocal.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1501-1508"},"PeriodicalIF":17.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141556973","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-08DOI: 10.1038/s41567-024-02561-6
Rhombohedral graphene is an emerging material with a rich correlated-electron phenomenology, including superconductivity. The magnetism of symmetry-broken trilayer graphene has now been explored, revealing important details of the physics and providing a roadmap for broader explorations of rhombohedral graphene.
{"title":"Revealing the complex phases of rhombohedral trilayer graphene","authors":"","doi":"10.1038/s41567-024-02561-6","DOIUrl":"10.1038/s41567-024-02561-6","url":null,"abstract":"Rhombohedral graphene is an emerging material with a rich correlated-electron phenomenology, including superconductivity. The magnetism of symmetry-broken trilayer graphene has now been explored, revealing important details of the physics and providing a roadmap for broader explorations of rhombohedral graphene.","PeriodicalId":19100,"journal":{"name":"Nature Physics","volume":"20 9","pages":"1379-1380"},"PeriodicalIF":17.6,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141556971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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