Pub Date : 2024-12-19DOI: 10.1038/s42005-024-01904-2
Rouven Essig, Ryan Plestid, Aman Singal
Solid-state detectors with a low energy threshold have several applications, including searches of non-relativistic halo dark-matter particles with sub-GeV masses. When searching for relativistic, beyond-the-Standard-Model particles with enhanced cross sections for small energy transfers, a small detector with a low energy threshold may have better sensitivity than a larger detector with a higher energy threshold. In this paper, we calculate the low-energy ionization spectrum from high-velocity particles scattering in a dielectric material. We consider the full material response including the excitation of bulk plasmons. We generalize the energy-loss function to relativistic kinematics, and benchmark existing tools used for halo dark-matter scattering against electron energy-loss spectroscopy data. Compared to calculations commonly used in the literature, such as the Photo-Absorption-Ionization model or the free-electron model, including collective effects shifts the recoil ionization spectrum towards higher energies, typically peaking around 4–6 electron-hole pairs. We apply our results to the three benchmark examples: millicharged particles produced in a beam, neutrinos with a magnetic dipole moment produced in a reactor, and upscattered dark-matter particles. Our results show that the proper inclusion of collective effects typically enhances a detector’s sensitivity to these particles, since detector backgrounds, such as dark counts, peak at lower energies. The authors calculate the low-energy excitation cross section for relativistic feebly interacting particles scattering from silicon detectors. This enables a search for millicharged particles using data collected by the SENSEI detector and opens a new path for applications of low-threshold semi-conductor detectors to search for new physics.
{"title":"Collective excitations and low-energy ionization signatures of relativistic particles in silicon detectors","authors":"Rouven Essig, Ryan Plestid, Aman Singal","doi":"10.1038/s42005-024-01904-2","DOIUrl":"10.1038/s42005-024-01904-2","url":null,"abstract":"Solid-state detectors with a low energy threshold have several applications, including searches of non-relativistic halo dark-matter particles with sub-GeV masses. When searching for relativistic, beyond-the-Standard-Model particles with enhanced cross sections for small energy transfers, a small detector with a low energy threshold may have better sensitivity than a larger detector with a higher energy threshold. In this paper, we calculate the low-energy ionization spectrum from high-velocity particles scattering in a dielectric material. We consider the full material response including the excitation of bulk plasmons. We generalize the energy-loss function to relativistic kinematics, and benchmark existing tools used for halo dark-matter scattering against electron energy-loss spectroscopy data. Compared to calculations commonly used in the literature, such as the Photo-Absorption-Ionization model or the free-electron model, including collective effects shifts the recoil ionization spectrum towards higher energies, typically peaking around 4–6 electron-hole pairs. We apply our results to the three benchmark examples: millicharged particles produced in a beam, neutrinos with a magnetic dipole moment produced in a reactor, and upscattered dark-matter particles. Our results show that the proper inclusion of collective effects typically enhances a detector’s sensitivity to these particles, since detector backgrounds, such as dark counts, peak at lower energies. The authors calculate the low-energy excitation cross section for relativistic feebly interacting particles scattering from silicon detectors. This enables a search for millicharged particles using data collected by the SENSEI detector and opens a new path for applications of low-threshold semi-conductor detectors to search for new physics.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-11"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01904-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142862478","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 : 2024-12-19DOI: 10.1038/s42005-024-01891-4
Elmer L. Gründeman, Vincent Barbé, Andrés Martínez de Velasco, Charlaine Roth, Mathieu Collombon, Julian J. Krauth, Laura S. Dreissen, Richard Taïeb, Kjeld S. E. Eikema
Laser spectroscopy of atomic hydrogen and hydrogen-like atoms is a powerful tool for tests of fundamental physics. The 1S–2S transition of hydrogen in particular is a cornerstone for stringent Quantum Electrodynamics (QED) tests and for an accurate determination of the Rydberg constant. We report laser excitation of the 1S–2S transition in singly-ionized helium (3He+), a hydrogen-like ion with much higher sensitivity to QED than hydrogen itself. The transition requires two-photon excitation in the challenging extreme ultraviolet wavelength range, which we achieve with a tabletop coherent laser system suitable for precision spectroscopy. The transition is excited by combining an ultrafast amplified pulse at 790 nm (derived from a frequency comb laser) with its 25th harmonic at 32 nm (produced by high-harmonic generation). The results are well described by our simulations and we achieve a sizable 2S excitation fraction of 10−4 per pulse, paving the way for future precision studies. A measurement of the 1S-2S transition frequency in He+ would enable fundamental physics tests, but the required extreme ultraviolet radiation makes this a challenge. The authors observe such transition using radiation produced by high-harmonic generation of frequency comb pulses, in a manner that is compatible with future precision spectroscopy.
{"title":"Laser excitation of the 1S–2S transition in singly-ionized helium","authors":"Elmer L. Gründeman, Vincent Barbé, Andrés Martínez de Velasco, Charlaine Roth, Mathieu Collombon, Julian J. Krauth, Laura S. Dreissen, Richard Taïeb, Kjeld S. E. Eikema","doi":"10.1038/s42005-024-01891-4","DOIUrl":"10.1038/s42005-024-01891-4","url":null,"abstract":"Laser spectroscopy of atomic hydrogen and hydrogen-like atoms is a powerful tool for tests of fundamental physics. The 1S–2S transition of hydrogen in particular is a cornerstone for stringent Quantum Electrodynamics (QED) tests and for an accurate determination of the Rydberg constant. We report laser excitation of the 1S–2S transition in singly-ionized helium (3He+), a hydrogen-like ion with much higher sensitivity to QED than hydrogen itself. The transition requires two-photon excitation in the challenging extreme ultraviolet wavelength range, which we achieve with a tabletop coherent laser system suitable for precision spectroscopy. The transition is excited by combining an ultrafast amplified pulse at 790 nm (derived from a frequency comb laser) with its 25th harmonic at 32 nm (produced by high-harmonic generation). The results are well described by our simulations and we achieve a sizable 2S excitation fraction of 10−4 per pulse, paving the way for future precision studies. A measurement of the 1S-2S transition frequency in He+ would enable fundamental physics tests, but the required extreme ultraviolet radiation makes this a challenge. The authors observe such transition using radiation produced by high-harmonic generation of frequency comb pulses, in a manner that is compatible with future precision spectroscopy.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-6"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01891-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142862430","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}
The rapid advancement of deep learning has motivated various analog computing devices for energy-efficient non-von Neuman computing. While recent demonstrations have shown their excellent performance, particularly in the inference phase, computation of training using analog hardware is still challenging due to the complexity of training algorithms such as backpropagation. Here, we present an alternative training algorithm that combines two emerging concepts: reservoir computing (RC) and biologically inspired training. Instead of backpropagated errors, the proposed method computes the error projection using nonlinear dynamics (i.e., reservoir), which is highly suitable for physical implementation because it only requires a single passive dynamical system with a smaller number of nodes. Numerical simulation with Lyapunov analysis showed some interesting features of our proposed algorithm itself: the reservoir basically should be selected to satisfy the echo-state-property; but even chaotic dynamics can be used for the training when its time scale is below the Lyapunov time; and the performance is maximized near the edge of chaos, which is similar to standard RC framework. Furthermore, we experimentally demonstrated the training of feedforward neural networks by using an optoelectronic reservoir computer. Our approach provides an alternative solution for deep learning computation and its physical acceleration. Existing training algorithms for deep neural networks are not suitable for energy-efficient analog hardware. Here, the authors propose and experimentally demonstrate an alternative training algorithm based on reservoir computing, which improves training efficiency in optoelectronic implementations.
{"title":"Reservoir direct feedback alignment: deep learning by physical dynamics","authors":"Mitsumasa Nakajima, Yongbo Zhang, Katsuma Inoue, Yasuo Kuniyoshi, Toshikazu Hashimoto, Kohei Nakajima","doi":"10.1038/s42005-024-01895-0","DOIUrl":"10.1038/s42005-024-01895-0","url":null,"abstract":"The rapid advancement of deep learning has motivated various analog computing devices for energy-efficient non-von Neuman computing. While recent demonstrations have shown their excellent performance, particularly in the inference phase, computation of training using analog hardware is still challenging due to the complexity of training algorithms such as backpropagation. Here, we present an alternative training algorithm that combines two emerging concepts: reservoir computing (RC) and biologically inspired training. Instead of backpropagated errors, the proposed method computes the error projection using nonlinear dynamics (i.e., reservoir), which is highly suitable for physical implementation because it only requires a single passive dynamical system with a smaller number of nodes. Numerical simulation with Lyapunov analysis showed some interesting features of our proposed algorithm itself: the reservoir basically should be selected to satisfy the echo-state-property; but even chaotic dynamics can be used for the training when its time scale is below the Lyapunov time; and the performance is maximized near the edge of chaos, which is similar to standard RC framework. Furthermore, we experimentally demonstrated the training of feedforward neural networks by using an optoelectronic reservoir computer. Our approach provides an alternative solution for deep learning computation and its physical acceleration. Existing training algorithms for deep neural networks are not suitable for energy-efficient analog hardware. Here, the authors propose and experimentally demonstrate an alternative training algorithm based on reservoir computing, which improves training efficiency in optoelectronic implementations.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-10"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01895-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845190","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 : 2024-12-19DOI: 10.1038/s42005-024-01885-2
Juan G. Restrepo, Clayton P. Byers, Per Sebastian Skardal
Identifying and suppressing unknown disturbances to dynamical systems is a problem with applications in many different fields. Here we present a model-free method to identify and suppress an unknown disturbance to an unknown system based only on previous observations of the system under the influence of a known forcing function. We find that, under very mild restrictions on the training function, our method is able to robustly identify and suppress a large class of unknown disturbances. We illustrate our scheme with the identification of both deterministic and stochastic unknown disturbances to an analog electric chaotic circuit and with numerical examples where a chaotic disturbance to various chaotic dynamical systems is identified and suppressed. Identifying and mitigating unknown disturbances to complex systems poses a critical challenge in a wide range of disciplines. Here, the authors use machine learning to identify unknown disturbances made to unknown systems and a methodology to suppress these disturbances to recover the undisturbed system.
{"title":"Suppressing unknown disturbances to dynamical systems using machine learning","authors":"Juan G. Restrepo, Clayton P. Byers, Per Sebastian Skardal","doi":"10.1038/s42005-024-01885-2","DOIUrl":"10.1038/s42005-024-01885-2","url":null,"abstract":"Identifying and suppressing unknown disturbances to dynamical systems is a problem with applications in many different fields. Here we present a model-free method to identify and suppress an unknown disturbance to an unknown system based only on previous observations of the system under the influence of a known forcing function. We find that, under very mild restrictions on the training function, our method is able to robustly identify and suppress a large class of unknown disturbances. We illustrate our scheme with the identification of both deterministic and stochastic unknown disturbances to an analog electric chaotic circuit and with numerical examples where a chaotic disturbance to various chaotic dynamical systems is identified and suppressed. Identifying and mitigating unknown disturbances to complex systems poses a critical challenge in a wide range of disciplines. Here, the authors use machine learning to identify unknown disturbances made to unknown systems and a methodology to suppress these disturbances to recover the undisturbed system.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-9"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01885-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142862424","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 : 2024-12-19DOI: 10.1038/s42005-024-01897-y
Shanshan Liu, Rhonald Burgos, Enze Zhang, Naizhou Wang, Xiao-Bin Qiang, Chuanzhao Li, Qihan Zhang, Z. Z. Du, Rui Zheng, Jingsheng Chen, Qing-Hua Xu, Kai Leng, Weibo Gao, Faxian Xiu, Dimitrie Culcer, Kian Ping Loh
The discovery of the nonlinear Hall effect provides an avenue for studying the interplay among symmetry, topology, and phase transitions, with potential applications in signal doubling and high-frequency rectification. However, practical applications require devices fabricated on large area thin film as well as room-temperature operation. Here, we demonstrate robust room-temperature nonlinear transverse response and microwave rectification in MnBi2Te4 films grown by molecular beam epitaxy. We observe multiple sign-reversals in the nonlinear response by tuning the chemical potential. Through theoretical analysis, we identify skew scattering and side jump, arising from extrinsic spin-orbit scattering, as the main mechanisms underlying the observed nonlinear signals. Furthermore, we demonstrate radio frequency (RF) rectification in the range of 1–8 gigahertz at 300 K. These findings not only enhance our understanding of the relationship between nonlinear response and magnetism, but also expand the potential applications as energy harvesters and detectors in high-frequency scenarios. The nonlinear Hall effect enables studies of symmetry and topology with potential in high-frequency devices, but practical applications demand room temperature operation. The authors report robust room temperature nonlinear transverse responses and microwave rectification (1–8 GHz) in MnBi2Te4 thin films, driven by extrinsic spin-orbit scattering.
{"title":"Room-temperature nonlinear transport and microwave rectification in antiferromagnetic MnBi2Te4 films","authors":"Shanshan Liu, Rhonald Burgos, Enze Zhang, Naizhou Wang, Xiao-Bin Qiang, Chuanzhao Li, Qihan Zhang, Z. Z. Du, Rui Zheng, Jingsheng Chen, Qing-Hua Xu, Kai Leng, Weibo Gao, Faxian Xiu, Dimitrie Culcer, Kian Ping Loh","doi":"10.1038/s42005-024-01897-y","DOIUrl":"10.1038/s42005-024-01897-y","url":null,"abstract":"The discovery of the nonlinear Hall effect provides an avenue for studying the interplay among symmetry, topology, and phase transitions, with potential applications in signal doubling and high-frequency rectification. However, practical applications require devices fabricated on large area thin film as well as room-temperature operation. Here, we demonstrate robust room-temperature nonlinear transverse response and microwave rectification in MnBi2Te4 films grown by molecular beam epitaxy. We observe multiple sign-reversals in the nonlinear response by tuning the chemical potential. Through theoretical analysis, we identify skew scattering and side jump, arising from extrinsic spin-orbit scattering, as the main mechanisms underlying the observed nonlinear signals. Furthermore, we demonstrate radio frequency (RF) rectification in the range of 1–8 gigahertz at 300 K. These findings not only enhance our understanding of the relationship between nonlinear response and magnetism, but also expand the potential applications as energy harvesters and detectors in high-frequency scenarios. The nonlinear Hall effect enables studies of symmetry and topology with potential in high-frequency devices, but practical applications demand room temperature operation. The authors report robust room temperature nonlinear transverse responses and microwave rectification (1–8 GHz) in MnBi2Te4 thin films, driven by extrinsic spin-orbit scattering.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-9"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01897-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845149","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 : 2024-12-19DOI: 10.1038/s42005-024-01899-w
Keita Funayama, Kenichi Yatsugi, Hideo Iizuka
Topological artificial crystals can exhibit one-way wave-propagation along the boundary with the wave being localized perpendicular to the boundary. The control of localization of such topological wave propagation is of great importance for enhancing coupling or avoiding unwanted coupling among neighboring boundaries toward topological integrated circuits. However, the effect of the geometry of topological boundaries on localization properties is not yet fully clear. Here, we experimentally and numerically demonstrate valley-topological transport on representative valley-topological boundaries with micro-electro-mechanical systems. We show that the zigzag and bridge boundaries, which have highly efficient wave transport, exhibit frequency independent and dependent wave localization, respectively. A simple analytic model is presented to capture the different behaviors of the two boundaries observed in the experiments. Our results provide opportunities to engineer frequency responses in topological circuits including frequency selective couplers through proper selection of boundary geometries. The authors numerically and experimentally investigate the transport properties of a quantum valley-Hall effect in a micro electromechanical system. The zigzag and bridge boundaries, which have highly efficient wave transport, exhibit frequency independent and dependent wave localization, respectively.
{"title":"Quantum valley Hall effect-based topological boundaries for frequency-dependent and -independent mode energy profiles","authors":"Keita Funayama, Kenichi Yatsugi, Hideo Iizuka","doi":"10.1038/s42005-024-01899-w","DOIUrl":"10.1038/s42005-024-01899-w","url":null,"abstract":"Topological artificial crystals can exhibit one-way wave-propagation along the boundary with the wave being localized perpendicular to the boundary. The control of localization of such topological wave propagation is of great importance for enhancing coupling or avoiding unwanted coupling among neighboring boundaries toward topological integrated circuits. However, the effect of the geometry of topological boundaries on localization properties is not yet fully clear. Here, we experimentally and numerically demonstrate valley-topological transport on representative valley-topological boundaries with micro-electro-mechanical systems. We show that the zigzag and bridge boundaries, which have highly efficient wave transport, exhibit frequency independent and dependent wave localization, respectively. A simple analytic model is presented to capture the different behaviors of the two boundaries observed in the experiments. Our results provide opportunities to engineer frequency responses in topological circuits including frequency selective couplers through proper selection of boundary geometries. The authors numerically and experimentally investigate the transport properties of a quantum valley-Hall effect in a micro electromechanical system. The zigzag and bridge boundaries, which have highly efficient wave transport, exhibit frequency independent and dependent wave localization, respectively.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-7"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01899-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845139","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 : 2024-12-19DOI: 10.1038/s42005-024-01861-w
Joseph Vimal Vas, Rohit Medwal, Sourabh Manna, Mayank Mishra, Aaron Muller, John Rex Mohan, Yasuhiro Fukuma, Martial Duchamp, Rajdeep Singh Rawat
Controlling the magnetic domain propagation is the key to realize ultrafast, high-density domain wall-based memory and logic devices for next generation computing. Two-Dimensional (2D) Van der Waals materials introduce localized modifications to the interfacial magnetic order, which could enable efficient control over the propagation of magnetic domains. However, there is limited direct experimental evidence and understanding of the underlying mechanism, for 2D material mediated control of domain wall propagation. Here, using Lorentz-Transmission Electron Microscopy (L-TEM) along with the Modified Transport of Intensity equations (MTIE), we demonstrate controlled domain expansion with in-situ magnetic field in a ferromagnet (Permalloy, NiFe) interfacing with a 2D VdW material Graphene (Gr). The Gr/NiFe interface exhibits distinctive domain expansion rate with magnetic field selectively near the interface which is further analysed using micromagnetic simulations. Our findings are crucial for comprehending direct visualization of interface controlled magnetic domain expansion, offering insights for developing future domain wall-based technology. This study explores how the interface between Permalloy and graphene affects the propagation of magnetic domains. Using advanced transmission electron microscopy and simulations, the research reveals key insights that could advance future memory and logic technologies.
{"title":"Direct visualization of local magnetic domain dynamics in a 2D Van der Walls material/ferromagnet interface","authors":"Joseph Vimal Vas, Rohit Medwal, Sourabh Manna, Mayank Mishra, Aaron Muller, John Rex Mohan, Yasuhiro Fukuma, Martial Duchamp, Rajdeep Singh Rawat","doi":"10.1038/s42005-024-01861-w","DOIUrl":"10.1038/s42005-024-01861-w","url":null,"abstract":"Controlling the magnetic domain propagation is the key to realize ultrafast, high-density domain wall-based memory and logic devices for next generation computing. Two-Dimensional (2D) Van der Waals materials introduce localized modifications to the interfacial magnetic order, which could enable efficient control over the propagation of magnetic domains. However, there is limited direct experimental evidence and understanding of the underlying mechanism, for 2D material mediated control of domain wall propagation. Here, using Lorentz-Transmission Electron Microscopy (L-TEM) along with the Modified Transport of Intensity equations (MTIE), we demonstrate controlled domain expansion with in-situ magnetic field in a ferromagnet (Permalloy, NiFe) interfacing with a 2D VdW material Graphene (Gr). The Gr/NiFe interface exhibits distinctive domain expansion rate with magnetic field selectively near the interface which is further analysed using micromagnetic simulations. Our findings are crucial for comprehending direct visualization of interface controlled magnetic domain expansion, offering insights for developing future domain wall-based technology. This study explores how the interface between Permalloy and graphene affects the propagation of magnetic domains. Using advanced transmission electron microscopy and simulations, the research reveals key insights that could advance future memory and logic technologies.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-6"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01861-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845141","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 : 2024-12-19DOI: 10.1038/s42005-024-01892-3
Gustavo Chaparro, Erich A. Müller
A longstanding challenge in thermodynamics has been the development of a unified analytical expression for the free energy of matter capable of describing all thermodynamic properties. Although significant strides have been made in modeling fluid phases using continuous equations of state (EoSs), the crystalline state has remained largely unexplored because of its complexity. This work introduces an approach that employs artificial neural networks to construct an EoS directly from comprehensive molecular simulation data. The efficacy of this method is demonstrated through application to the Mie potential, resulting in a thermodynamically consistent model seamlessly bridging fluid and crystalline phases. The proposed EoS accurately predicts metastable regions, enabling a comprehensive characterization of the phase diagram, which includes the critical and triple points. The article presents an equation of state (EoS) for fluid and solid phases using artificial neural networks. This EoS accurately models thermophysical properties and predicts phase transitions, including the critical and triple points. This approach offers a unified way to understand different states of matter.
{"title":"Development of a Helmholtz free energy equation of state for fluid and solid phases via artificial neural networks","authors":"Gustavo Chaparro, Erich A. Müller","doi":"10.1038/s42005-024-01892-3","DOIUrl":"10.1038/s42005-024-01892-3","url":null,"abstract":"A longstanding challenge in thermodynamics has been the development of a unified analytical expression for the free energy of matter capable of describing all thermodynamic properties. Although significant strides have been made in modeling fluid phases using continuous equations of state (EoSs), the crystalline state has remained largely unexplored because of its complexity. This work introduces an approach that employs artificial neural networks to construct an EoS directly from comprehensive molecular simulation data. The efficacy of this method is demonstrated through application to the Mie potential, resulting in a thermodynamically consistent model seamlessly bridging fluid and crystalline phases. The proposed EoS accurately predicts metastable regions, enabling a comprehensive characterization of the phase diagram, which includes the critical and triple points. The article presents an equation of state (EoS) for fluid and solid phases using artificial neural networks. This EoS accurately models thermophysical properties and predicts phase transitions, including the critical and triple points. This approach offers a unified way to understand different states of matter.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-9"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01892-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845168","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}
Mixing the fundamental (ω) and the second harmonic (2ω) waves in the gas phase is a widely employed technique for emitting terahertz (THz) pulses. The THz generation driven by bi-chromatic fields can be described by the photocurrent model, where the THz generation is attributed to free electrons ionized by the ω field, and the 2ω field provides a perturbation to break the symmetry of the asymptotic momentum of free electrons. However, we find that the THz radiation is amplified by one order of magnitude when driven by bi-focal bi-chromatic fields, which cannot be explained only using the photocurrent model. Meanwhile, present measurements demonstrate that the THz radiation mainly originates from the plasma created by the 2ω pulses instead of the ω pulses. Energy transfer from the 2ω beam to the THz beam during the THz generation has been observed, validating the major contribution of the 2ω beam. Furthermore, the THz bandwidth has been observed to extensively exceed the bandwidth of the pump pulse, not be explained by the photocurrent model as well. These counterintuitive results present a significant challenge for understanding strong-field nonlinear optics and simultaneously expanding various applications. Mixing the fundamental (ω) and the second harmonic (2ω) waves in the gas phase is a widely used technique for generating terahertz pulses. The authors experimentally present an enhanced terahertz emission through the temporal-spatial manipulation of bi-focal bi-chromatic fields, and the THz radiation mainly originates from the plasma created by the 2ω pulses instead of the ω pulses, which cannot be explained only using photocurrent model.
{"title":"Temporal-spatial manipulation of bi-focal bi-chromatic fields for terahertz radiations","authors":"Jingjing Zhao, Yizhu Zhang, Yanjun Gao, Meng Li, Xiaokun Liu, Weimin Liu, Tian-Min Yan, Yuhai Jiang","doi":"10.1038/s42005-024-01893-2","DOIUrl":"10.1038/s42005-024-01893-2","url":null,"abstract":"Mixing the fundamental (ω) and the second harmonic (2ω) waves in the gas phase is a widely employed technique for emitting terahertz (THz) pulses. The THz generation driven by bi-chromatic fields can be described by the photocurrent model, where the THz generation is attributed to free electrons ionized by the ω field, and the 2ω field provides a perturbation to break the symmetry of the asymptotic momentum of free electrons. However, we find that the THz radiation is amplified by one order of magnitude when driven by bi-focal bi-chromatic fields, which cannot be explained only using the photocurrent model. Meanwhile, present measurements demonstrate that the THz radiation mainly originates from the plasma created by the 2ω pulses instead of the ω pulses. Energy transfer from the 2ω beam to the THz beam during the THz generation has been observed, validating the major contribution of the 2ω beam. Furthermore, the THz bandwidth has been observed to extensively exceed the bandwidth of the pump pulse, not be explained by the photocurrent model as well. These counterintuitive results present a significant challenge for understanding strong-field nonlinear optics and simultaneously expanding various applications. Mixing the fundamental (ω) and the second harmonic (2ω) waves in the gas phase is a widely used technique for generating terahertz pulses. The authors experimentally present an enhanced terahertz emission through the temporal-spatial manipulation of bi-focal bi-chromatic fields, and the THz radiation mainly originates from the plasma created by the 2ω pulses instead of the ω pulses, which cannot be explained only using photocurrent model.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":" ","pages":"1-6"},"PeriodicalIF":5.4,"publicationDate":"2024-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01893-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142845191","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 : 2024-12-19DOI: 10.1038/s42005-024-01863-8
Aydin Ashrafi-Belgabad, Reza Karimi, Mohammad Monfared, Kaili Tian, Parviz Parvin, Benji Wales, Éric Bisson, Samuel Beaulieu, Mathieu Giguère, Jean-Claude Kieffer, Philippe Lassonde, François Légaré, Heide Ibrahim, Joseph H. Sanderson
Coulomb explosion is an established momentum imaging technique, where the molecules are ionized multiple times on a femtosecond time scale before breaking up into ionized fragments. By measuring the momentum of all the ions, information about the initial molecular structure is theoretically available. However, significant geometric changes due to multiple ionizations occur before the explosion, posing a challenge in retrieving the ground-state structure of molecules from the measured momentum values of the fragments. In this work, we investigate theoretically and experimentally such a connection between the ground-state geometry of a polyatomic molecule (OCS) and the detected momenta of ionic fragments from the Coulomb explosion. By relying on time-dependent density functional theory (TDDFT), we can rigorously model the ionization dynamics of the molecule in the tunneling regime. We reproduce the energy release and the Newton plot momentum patterns of an experiment in which OCS is ionized to the 6+ charge state. Our results provide insight into the behavior of molecules during strong field multiple ionization, opening a way toward precision imaging of real-space molecular geometries using tabletop lasers. Understanding molecular structure and dynamics through strong-field laser interactions holds great promise. The authors use quantum calculations to show how bonds and angles evolve in an OCS molecule ionized six times by a 7 fs, 800 nm laser pulse, accurately predicting our experimental results.
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