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MAGUS: machine learning and graph theory assisted universal structure searcher

national Science Review 2023年第7期10卷 213-233页

作者： Junjie Wang Hao Gao Yu Han Chi Ding Shuning Pan Yong Wang Qiuhan Jia Hui-Tian Wang Dingyu Xing Jian Sun national laboratory of solid state microstructures School of Physics and Collaborative Innovation Center of Advanced Microstructures Nanjing University

Crystal structure predictions based on first-principles calculations have gained great success in materials science and solid state physics.However,the remaining challenges still limit their applications in systems with a large number of atoms,especially the complexity of conformational space and the cost of local optimizations for big systems.Here,we introduce a crystal structure prediction method,MAGUS,based on the evolutionary algorithm,which addresses the above challenges with machine learning and graph theory.Techniques used in the program are summarized in detail and benchmark tests are provided.With intensive tests,we demonstrate that on-the-fly machine-learning potentials can be used to significantly reduce the number of expensive first-principles calculations,and the crystal decomposition based on graph theory can efficiently decrease the required configurations in order to find the target structures.We also summarized the representative applications of this method on several research topics,including unexpected compounds in the interior of planets and their exotic states at high pressure and high temperature(superionic,plastic,partially diffusive state,etc.);new functional materials(superhard,high-energy-density,superconducting,photoelectric materials),etc.These successful applications demonstrated that MAGUS code can help to accelerate the discovery of interesting materials and phenomena,as well as the significant value of crystal structure predictions in general.

关键词： crystal structure searching materials design ab-initio calculations density functional theory high-pressure phase transition

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Versatile platform of nonlocal metasurfaces for both spectral and spatial control of lightt waves

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Light(Science & Applications) 2022年第11期11卷 2553-2555页

作者： Run Chen Shuming Wang national laboratory of solid-state microstructures School of PhysicsNanjing UniversityNanjing 210093China

Multifunctional nonlocal metasurfaces based on quasi-bound states in the continuum are experimentally demonstrated,which shapes the wavefronts at the resonant wavelengths while have no effect on other wavelengths.By means of cascade and orthogonal perturbations,the nonlocal metasurface devices can be extended to a versatile platform with multifunction.

关键词： surfaces nonlocal versatile

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钾氨电子化合物中的准二维自旋-派尔斯相变

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Science Bulletin 2024年第8期69卷 1027-1036页

作者：丁驰鲁清郭照芃黄天衡王俊杰韩瑜邢定钰孙建 national laboratory of solid state microstructures School of Physics and Collaborative Innovation Center of Advanced MicrostructuresNanjing UniversityNanjing 210093China

Electron-phonon interactions and electron-electron correlations represent two crucial facets of condensed matter physics.For instance,in a half-filled spin-1/2 anti-ferromagnetic chain,the lattice dimerization induced by electron-nucleus interaction can be intensified by onsite Coulomb repulsion,resulting in a spin-Peierls state.Through first-principles calculations and crystal structure prediction methods,we have identified that under mild pressures,potassium and ammonia can form stable compounds:R3m K(NH_(3))_(2),Pm3 m K(NH_(3))_(2),and Cm K_(2)(NH_(3))_(3).Our predictions suggest that the R3 m K(NH_(3))_(2)exhibits electride characteristics,marked by the formation of interstitial anionic electrons(IAEs)in the interlayer space.These IAEs are arranged in quasi-two-dimensional triangular arrays.With increasing pressure,the electronic van-Hove singularity shifts toward the Fermi level,resulting in an augmented density of states and the onset of both Peierls and magnetic instabilities.Analyzing these instabilities,we determine that the ground state of the R3 m K(NH_(3))_(2)is the dimerized P2_(1)/m phase with zigzag-type anti-ferromagnetic IAEs.This state can be described by the triangular-lattice antiferromagnetic Heisenberg model with modulated magnetic interactions.Furthermore,we unveil the coexistence and positive interplay between magnetic and Peierls instability,constituting a scenario of spin-Peierls instability unprecedented in realistic 2D materials,particularly involving IAEs.This work provides valuable insights into the coupling of IAEs with the adjacent lattice and their spin correlations in quantum materials.

关键词： Quasi-two-dimensional Interstitial anionic electrons Potassium ammonia compounds Spin-Peierls transition Antiferromagnetism

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Experimental quantum secure network with digital signatures and encryption

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national Science Review 2023年第4期10卷 86-96页

作者： Hua-Lei Yin Yao Fu Chen-Long Li Chen-Xun Weng Bing-Hong Li Jie Gu Yu-Shuo Lu Shan Huang Zeng-Bing Chen national laboratory of solid state microstructures School of Physics Collaborative Innovation Center of Advanced Microstructures Nanjing University MatricTime Digital Technology Co.Ltd.

Cryptography promises four information security objectives, namely, confidentiality, integrity, authenticity and non-repudiation, to support trillions of transactions annually in the digital economy. Efficient digital signatures, ensuring integrity, authenticity and non-repudiation of data with information-theoretical security are highly urgent and intractable open problems in cryptography. Here, we propose a high-efficiency quantum digital signature(QDS) protocol using asymmetric quantum keys acquired via secret sharing, one-time universal2hashing and a one-time pad. We just need to use a 384-bit key to sign documents of lengths up to 264with a security bound of 10-19. If a one-megabit document is signed, the signature efficiency is improved by more than 108times compared with previous QDS protocols.Furthermore, we build the first all-in-one quantum secure network integrating information-theoretically secure communication, digital signatures, secret sharing and conference key agreement and experimentally demonstrate this signature efficiency advantage. Our work completes the cryptography toolbox of the four information security objectives.

关键词： quantum digital signature information-theoretical security secret sharing one-time universal2 hashing cryptography toolbox

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Demonstration of superadiabatic population transfer in superconducting qubit

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Chinese physics B 2018年第6期27卷 251-256页

作者：李蒙蒙谭新生戴坤哲赵鹏于海峰于扬 national laboratory of solid state microstructures School of Physics Nanjing University

We implemented the superadiabatic population transfer within the nonadiabatic regime in a two-level superconducting qubit system. To realize the superadiabatic procedure, we added an additional term in the Hamiltonian, introducing an auxiliary counter-diabatic field to cancel the nonadiabatic contribution in the evolution. Based on the superadiabatic procedure, we further demonstrated quantum Phase and NOT gates. These operations, which possess both of the fast and robust features, are promising for quantum information processing.

关键词： superadiabatic superconducting qubit counter-diabatic fast evolution

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A novel superhard tungsten nitride predicted by machine-learning accelerated crystal structure search

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Science Bulletin 2018年第13期63卷 817-824页

作者： Kang Xia Hao Gao Cong Liu Jianan Yuan Jian Sun Hui-Tian Wang Dingyu Xing national laboratory of solid state microstructures School of Physics and Collaborative Innovation Center of Advanced MicrostructuresNanjing University

Transition metal nitrides have been suggested to have both high hardness and good thermal stability with large potential application value,but so far stable superhard transition metal nitrides have not been synthesized.Here,with our newly developed machine-learning accelerated crystal structure searching method,we designed a superhard tungsten nitride,h-WN_6,which can be synthesized at pressure around65 GPa and quenchable to ambient pressure.This h-WN_6is constructed with single-bonded armchair-like N_6rings and presents ionic-like features,which can be formulated as W^(2.4+)N_6^(2.4à).It has a band gap of1.6 e V at 0 GPa and exhibits an abnormal gap broadening behavior under pressure.Excitingly,this h-WN_6is found to be the hardest among transition metal nitrides known so far(Vickers hardness around57 GPa)and also has a very high melting temperature(around 1,900 K).Additionally,the good gravimetric(3.1 k J/g)and volumetric(28.0 k J/cm^3)energy densities make this nitrogen-rich compound a potential high-energy-density material.These predictions support the designing rules and may stimulate future experiments to synthesize superhard and high-energy-density material.

关键词：金属氮化物水晶结构预言机器学习搜索钨热稳定性

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Recent progress in molten salt synthesis of low-dimensional perovskite oxide nanostructures, structural characterization,properties, and functional applications: A review

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Journal of Materials Science & Technology 2018年第6期34卷 914-930页

作者： Piaojie Xue Heng Wu Yao Lu Xinhua Zhu national laboratory of solid state microstructures School of Physics Nanjing University

Molten salt synthesis （MSS） method has advantages of the simplicity in the process equipment, versatile and large-scale synthesis, and friendly environment, which provides an excellent approach to synthesize high pure oxide powders with controllable compositions and morphologies. Among these oxides, perovskite oxides with a composition of ABO3 exhibit a broad spectrum of physical properties and functions （e.g. ferroelectric, piezoelectric, magnetic, photovoltaic and photocatalytic properties）. The downscaling of the spatial geometry of perovskite oxides into nanometers result in novel properties that are different from the bulk and film counterparts. Recent interest in nanoscience and nanotechnology has led to great efforts focusing on the synthesis of low-dimensional perovskite oxide nanostructures （PONs） to better understand their novel physical properties at nanoscale. Therefore, the low-dimensional PONs such as perovskite nanoparticles, nanowires, nanorods, nanotubes, nanofibers, nanobelts, and two dimensional oxide nanostructures, play an important role in developing the next generation of oxide electronics. In the past few years, much effort has been made on the synthesis of PONs by MSS method and their structural characterizations. The functional applications of PONs are also explored in the fields of storage memory, energy harvesting, and solar energy conversion. This review summarizes the recent progress in the synthesis of low-dimensional PONs by MSS method and its modified ways. Their structural char- acterization and physical properties are also scrutinized. The potential applications of low-dimensional PONs in different fields such as data memory and storage, energy harvesting, solar energy conversion, are highlighted. Perspectives concerning the future research trends and challenges of low-dimensional PONs are also outlined. ~ 2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.

关键词： Low-dimensional perovskite nanostructures Molten salt synthesis Structural characterization Physical properties Functional applications

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Generalized Drude model and electromagnetic screening in metals and superconductors

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Chinese physics B 2018年第5期27卷 453-457页

作者：王达 national laboratory of solid state microstructures & school of physics Nanjing University

Electromagnetic screening is studied from the perspective of fluid mechanics by generalizing the Drude theory, which unifies three known results： Thomas–Fermi screening of the longitudinal field in both metals and superconductors, the skin effect of the transverse field in metals, and the Meissner effect in superconductors. In the special case of superfluid electrons, we slightly generalize the London equations to incorporate the longitudinal electric fields. Moreover, regarding the experiments, our study points out that the dynamical measurement may overestimate the superfluid density.

关键词： electromagnetic screening Thomas-Fermi screening London penetration depth Meissner effect

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Stochastic spin-orbit-torque device as the STDP synapse for spiking neural networks

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Science China(physics,Mechanics & Astronomy) 2023年第5期66卷 188-194页

作者： Haotian Li Liyuan Li Kaiyuan Zhou Chunjie Yan Zhenyu Gao Zishuang Li Ronghua Liu national laboratory of solid state microstructures Jiangsu Provincial Key Laboratory for NanotechnologySchool of PhysicsNanjing UniversityNanjing 210093China

Neuromorphic hardware,as a non-Von Neumann architecture,has better energy efficiency and parallelism than the conventional computer.Here,with the numerical modeling spin-orbit torque(SOT)device using current-induced SOT and Joule heating effects,we acquire its magnetization stochastic switching probability as a function of the interval time of input current pulses and use it to mimic the spike-timing-dependent plasticity learning behavior like actual brain working.We further demonstrate that the artificial spiking neural network(SNN)built by this SOT device can perform unsupervised handwritten digit recognition with an accuracy of 80%and logic operation learning.Our work provides a new clue to achieving SNN-based neuromorphic hardware using high-energy efficiency and nonvolatile spintronics nanodevices.

关键词： spin-orbit torque neuromorphic hardware spiking neural network stochastic magnetization reversal

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Fabrication of Al air-bridge on coplanar waveguide

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Chinese physics B 2018年第10期27卷 216-218页

作者：金震川吴海腾于海峰于扬 national laboratory of solid state microstructures School of PhysicsNanjing University

Superconducting coplanar waveguide（CPW） can be widely used as two-dimensional（2 D） resonator, transmission line or feedline, providing an important component for superconducting quantum circuit which is a promising candidate for quantum information processing. Due to the discontinuities and asymmetries in the ground planes, CPW usually exhibits the spurious resonance, which is a common source of decoherence in circuit quantum electrodynamics experiments. To mitigate the spurious resonance, we fabricated superconducting aluminum air-bridges on Nb CPW. The fabricated airbridges are approximately 3 m high and up to 120 m long. Compared with other methods, the fabrication procedures of our air-bridges are simpler, and the air-bridge can withstand strong ultrasound.

关键词： air-bridge fabrication superconducting coplanar waveguide

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