The hydrogen bond(HB) is an important type of intermolecular interaction, which is generally weak, ubiquitous,and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum me...The hydrogen bond(HB) is an important type of intermolecular interaction, which is generally weak, ubiquitous,and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects(NQEs) on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice.展开更多
Opto–electromechanical coupling at the nanoscale is an important topic in new scientific studies and technical applications. In this work, the optically manipulated electromechanical behaviors of individual cadmium s...Opto–electromechanical coupling at the nanoscale is an important topic in new scientific studies and technical applications. In this work, the optically manipulated electromechanical behaviors of individual cadmium sulfide(CdS) nanowires are investigated by a customer-built optical holder inside transmission electron microscope, wherein in situ electromechanical resonance took place in conjunction with photo excitation. It is found that the natural resonance frequency of the nanowire under illumination becomes considerably lower than that under darkness. This redshift effect is closely related to the wavelength of the applied light and the diameter of the nanowires. Density functional theory(DFT) calculation shows that the photoexcitation leads to the softening of CdS nanowires and thus the redshift of natural frequency, which is in agreement with the experimental results.展开更多
The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time a...The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time and T is the temperature. In many glassforming liquids, the breakdown of SE relation often occurred when the dynamics of the liquids becomes glassy, and its origin is still debated among many scientists. Using molecular dynamics simulations and support-vector machine method, it is found that the scaling between diffusion and relaxation fails when the total population of solid-like clusters shrinks at the maximal rate with decreasing temperature, which implies a dramatic unification of clusters into an extensive dominant one occurs at the time of breakdown of the SE relation. Our data leads to an interpretation that the SE violation in metallic glass-forming liquids can be attributed to a specific change in the atomic structures.展开更多
The defects in the ceria usually work as the active reaction sites in their industrial applications.In this article,we studied the formation and atomic process of the defects of ceria nanowires under heating by using ...The defects in the ceria usually work as the active reaction sites in their industrial applications.In this article,we studied the formation and atomic process of the defects of ceria nanowires under heating by using in situ aberration-corrected transmission electron microscopy(Cs-TEM)method.With the temperature elevating,ceria nanowires are reduced and defects begin to appear and grow up.When temperature reaches 1,023 K,the defect morphology exhibits the rhombus or hexagon patterns,which are surrounded by{111}and{200}planes with lower surface energy,and the heated ceria still maintain the same cubic fluorite structure as their parent.It is also indicated that the formation of defects originates from the release of lattice oxygen and the volatilization of surface Ce ions.This work provides an important insight into designing ceria-based catalysts and ionic conductors.展开更多
The dynamic behavior of the interface between few layer graphene(FLG) and tungsten metal tips under Joule heating has been studied by in-situ transmission electron microscopy(TEM) method. High-resolution and real-time...The dynamic behavior of the interface between few layer graphene(FLG) and tungsten metal tips under Joule heating has been studied by in-situ transmission electron microscopy(TEM) method. High-resolution and real-time observations show the tungsten tip ‘swallow' carbon atoms of the FLG and ‘spit' graphite shells at its surface. The tip was carbonized to tungsten carbide(WC, W_2 C and WC_x) after this process. A carbon diffusion mechanism has been proposed based on the diffusion of carbon atoms through the tungsten tip and separation from the surface of the tip. After Joule heating, the initial FLG-metal mechanical contact was transformed to FLG-WCx-W contact, which results in significant improvement on electrical conductivity at the interface.展开更多
Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with s...Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.展开更多
The notion of topological phases extended to dynamical systems stimulates extensive studies,of which the characterization of nonequilibrium topological invariants is a central issue and usually necessitates the inform...The notion of topological phases extended to dynamical systems stimulates extensive studies,of which the characterization of nonequilibrium topological invariants is a central issue and usually necessitates the information of quantum dynamics in both the time and momentum dimensions.Here,we propose the topological holographic quench dynamics in synthetic dimension,and also show it provides a highly efficient scheme to characterize photonic topological phases.A pseudospin model is constructed with ring resonators in a synthetic lattice formed by frequencies of light,and the quench dynamics is induced by initializing a trivial state,which evolves under a topological Hamiltonian.Our key prediction is that the complete topological information of the Hamiltonian is encoded in quench dynamics solely in the time dimension,and is further mapped to lower-dimensional space,manifesting the holographic features of the dynamics.In particular,two fundamental time scales emerge in the dynamical evolution,with one mimicking the topological band on the momentum dimension and the other characterizing the residue time evolution of the state after the quench.For this,a universal duality between the quench dynamics and the equilibrium topological phase of the spin model is obtained in the time dimension by extracting information from the field evolution dynamics in modulated ring systems in simulations.This work also shows that the photonic synthetic frequency dimension provides an efficient and powerful way to explore the topological nonequilibrium dynamics.展开更多
A Kramers pair of helical edge states in quantum spin Hall effect(QSHE) is robust against normal dephasing but not robust to spin dephasing. In our work, we provide an effective spin dephasing mechanism in the puddles...A Kramers pair of helical edge states in quantum spin Hall effect(QSHE) is robust against normal dephasing but not robust to spin dephasing. In our work, we provide an effective spin dephasing mechanism in the puddles of two-dimensional(2D) QSHE, which is simulated as quantum dots modeled by 2D massive Dirac Hamiltonian. We demonstrate that the spin dephasing effect can originate from the combination of the Rashba spin-orbit coupling and electron-phonon interaction, which gives rise to inelastic backscattering in edge states within the topological insulator quantum dots, although the time-reversal symmetry is preserved throughout. Finally,we discuss the tunneling between extended helical edge states and local edge states in the QSH quantum dots, which leads to backscattering in the extended edge states. These results can explain the more robust edge transport in In As/Ga Sb QSH systems.展开更多
Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport...Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices,which generate extensive interest in the last decade.Dephasing is the process of the loss of phase coherence,which inevitably exists in a realistic sample.In this review,we focus on recent progress in dephasing effects on the topological insulators.In general,there are two types of dephasing processes:normal dephasing and spin dephasing.In two-dimensional topological insulators,the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin dephasing.Several microscopic mechanisms of spin dephasing are then discussed.In three-dimensional topological insulators,the helical surface states exhibit a helical spin texture due to the spin-momentum locking mechanism.Thus,normal dephasing has close connection to spin dephasing in this case,and gives rise to anomalous "gap-like" feature.Dephasing effects on properties of helical surface states are investigated.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11275008,91021007,and 10974012)the China Postdoctoral Science Foundation(Grant No.2014M550005)
文摘The hydrogen bond(HB) is an important type of intermolecular interaction, which is generally weak, ubiquitous,and essential to life on earth. The small mass of hydrogen means that many properties of HBs are quantum mechanical in nature. In recent years, because of the development of computer simulation methods and computational power, the influence of nuclear quantum effects(NQEs) on the structural and energetic properties of some hydrogen bonded systems has been intensively studied. Here, we present a review of these studies by focussing on the explanation of the principles underlying the simulation methods, i.e., the ab initio path-integral molecular dynamics. Its extension in combination with the thermodynamic integration method for the calculation of free energies will also be introduced. We use two examples to show how this influence of NQEs in realistic systems is simulated in practice.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21773303,21872172,51472267,and 51421002)the Chinese Academy of Sciences(Grant Nos.ZDYZ2015-1,XDB30000000,and XDB07030100)
文摘Opto–electromechanical coupling at the nanoscale is an important topic in new scientific studies and technical applications. In this work, the optically manipulated electromechanical behaviors of individual cadmium sulfide(CdS) nanowires are investigated by a customer-built optical holder inside transmission electron microscope, wherein in situ electromechanical resonance took place in conjunction with photo excitation. It is found that the natural resonance frequency of the nanowire under illumination becomes considerably lower than that under darkness. This redshift effect is closely related to the wavelength of the applied light and the diameter of the nanowires. Density functional theory(DFT) calculation shows that the photoexcitation leads to the softening of CdS nanowires and thus the redshift of natural frequency, which is in agreement with the experimental results.
基金the National Natural Science Foundation of China(Grant Nos.11804027,and 11525520)the National Basic Research Program of China(Grant No.2015CB856801)the Fundamental Research Funds for the Central Universities(Grant No.2018NTST24).
文摘The Stokes-Einstein(SE) relation has been considered as one of the hallmarks of dynamics in liquids. It describes that the diffusion constant D is proportional to(τ/T)–1, where τ is the structural relaxation time and T is the temperature. In many glassforming liquids, the breakdown of SE relation often occurred when the dynamics of the liquids becomes glassy, and its origin is still debated among many scientists. Using molecular dynamics simulations and support-vector machine method, it is found that the scaling between diffusion and relaxation fails when the total population of solid-like clusters shrinks at the maximal rate with decreasing temperature, which implies a dramatic unification of clusters into an extensive dominant one occurs at the time of breakdown of the SE relation. Our data leads to an interpretation that the SE violation in metallic glass-forming liquids can be attributed to a specific change in the atomic structures.
基金supported by the Program from Chinese Academy of Sciences (ZDYZ2015-1, XDB30000000,XDB07030100, Y8K5261B11)the National Natural Science Foundation of China (21773303, 21872172, 51472267, 51672007, 221322304, 11290161, 51572233, 61574121, 51421002)+1 种基金the National Key Research and Development Program (2016YFA0300804, 2016YFA0300903)the National Program for Thousand Young Talents of China
文摘The defects in the ceria usually work as the active reaction sites in their industrial applications.In this article,we studied the formation and atomic process of the defects of ceria nanowires under heating by using in situ aberration-corrected transmission electron microscopy(Cs-TEM)method.With the temperature elevating,ceria nanowires are reduced and defects begin to appear and grow up.When temperature reaches 1,023 K,the defect morphology exhibits the rhombus or hexagon patterns,which are surrounded by{111}and{200}planes with lower surface energy,and the heated ceria still maintain the same cubic fluorite structure as their parent.It is also indicated that the formation of defects originates from the release of lattice oxygen and the volatilization of surface Ce ions.This work provides an important insight into designing ceria-based catalysts and ionic conductors.
基金supported by the Program from Ministry of Science and Technology(Grant Nos.2012CB933003,2013CB932600,2013CB934500&2013YQ16055107)the National Natural Science Foundation of China(Grant Nos.11474337,221322304,51172273&51421002)Strategic Priority Research Program B of the Chinese Academy of Sciences of China(Grant No.XDB07030100)
文摘The dynamic behavior of the interface between few layer graphene(FLG) and tungsten metal tips under Joule heating has been studied by in-situ transmission electron microscopy(TEM) method. High-resolution and real-time observations show the tungsten tip ‘swallow' carbon atoms of the FLG and ‘spit' graphite shells at its surface. The tip was carbonized to tungsten carbide(WC, W_2 C and WC_x) after this process. A carbon diffusion mechanism has been proposed based on the diffusion of carbon atoms through the tungsten tip and separation from the surface of the tip. After Joule heating, the initial FLG-metal mechanical contact was transformed to FLG-WCx-W contact, which results in significant improvement on electrical conductivity at the interface.
基金This work was supported by the National Basic Research Program of China under Grant No. 2015CB856801, the National Natural Science Foundation of China under Grant Nos. 11525520 and 11290162/A040106, and the National Key R＆D Program under Grant No. 2016YFA0300901. The computer re- sources for this study were provided by the Arkansas High Per- formance Computational Center through grant MRI-R2 0959124 provided by the NSF of USA.
基金supported by the National Basic Research Program of China(Grant Nos.2015CB921102,2017YFA0303301,and 2017YFA0304600)National Natural Science Foundation of China(Grant Nos.11504008,11574245,11674028,and 11822407)
文摘Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.
基金supported by the National Natural Science Foundation of China (11825401, 11761161003, and 11921005)the National Key R&D Program of China (2016YFA0301604)Strategic Priority Research Program of CAS (XDB28000000)。
基金This paper was supported by the National Natural Science Foundation of China(11974245,11825401,and 11761161003)National Key R&D Program of China(2017YFA0303701)+3 种基金Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)Natural Science Foundation of Shanghai(19ZR1475700)by the Open Project of Shenzhen Institute of Quantum Science and Engineering(Grant No.SIQSE202003)L.Y.acknowledges support from the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning.X.C.also acknowledges the support from Shandong Quancheng Scholarship(00242019024).
文摘The notion of topological phases extended to dynamical systems stimulates extensive studies,of which the characterization of nonequilibrium topological invariants is a central issue and usually necessitates the information of quantum dynamics in both the time and momentum dimensions.Here,we propose the topological holographic quench dynamics in synthetic dimension,and also show it provides a highly efficient scheme to characterize photonic topological phases.A pseudospin model is constructed with ring resonators in a synthetic lattice formed by frequencies of light,and the quench dynamics is induced by initializing a trivial state,which evolves under a topological Hamiltonian.Our key prediction is that the complete topological information of the Hamiltonian is encoded in quench dynamics solely in the time dimension,and is further mapped to lower-dimensional space,manifesting the holographic features of the dynamics.In particular,two fundamental time scales emerge in the dynamical evolution,with one mimicking the topological band on the momentum dimension and the other characterizing the residue time evolution of the state after the quench.For this,a universal duality between the quench dynamics and the equilibrium topological phase of the spin model is obtained in the time dimension by extracting information from the field evolution dynamics in modulated ring systems in simulations.This work also shows that the photonic synthetic frequency dimension provides an efficient and powerful way to explore the topological nonequilibrium dynamics.
基金supported by the National Basic Research Program of China(Grant Nos.2015CB921102,2012CB821402 and 2012CB921303)the National Natural Science Foundation of China(Grant Nos.11534001 and11274364)
文摘A Kramers pair of helical edge states in quantum spin Hall effect(QSHE) is robust against normal dephasing but not robust to spin dephasing. In our work, we provide an effective spin dephasing mechanism in the puddles of two-dimensional(2D) QSHE, which is simulated as quantum dots modeled by 2D massive Dirac Hamiltonian. We demonstrate that the spin dephasing effect can originate from the combination of the Rashba spin-orbit coupling and electron-phonon interaction, which gives rise to inelastic backscattering in edge states within the topological insulator quantum dots, although the time-reversal symmetry is preserved throughout. Finally,we discuss the tunneling between extended helical edge states and local edge states in the QSH quantum dots, which leads to backscattering in the extended edge states. These results can explain the more robust edge transport in In As/Ga Sb QSH systems.
基金supported by the National Key Research and Development Program of China(2021YFA1400900)the National Natural Science Foundation of China(11825401 and 11921005)+1 种基金the Open Project of Shenzhen Institute of Quantum Science and Engineering(SIQSE202003)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB28000000)。
基金We are grateful to Y. Q. Li, Q. F. Sun and S. G. Cheng for collaboration and for their important contributions reviewed in this paper.supported by the National Natural Science Foundation of China (Grant Nos.11534001,11822407,and 11674028)NBRPC (Grant Nos. 2017YFA0303301 and 2017YFA0304600)NSF of Jiangsu Province,China (Grant No. BK20160007).H.Jiang was also funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices,which generate extensive interest in the last decade.Dephasing is the process of the loss of phase coherence,which inevitably exists in a realistic sample.In this review,we focus on recent progress in dephasing effects on the topological insulators.In general,there are two types of dephasing processes:normal dephasing and spin dephasing.In two-dimensional topological insulators,the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin dephasing.Several microscopic mechanisms of spin dephasing are then discussed.In three-dimensional topological insulators,the helical surface states exhibit a helical spin texture due to the spin-momentum locking mechanism.Thus,normal dephasing has close connection to spin dephasing in this case,and gives rise to anomalous "gap-like" feature.Dephasing effects on properties of helical surface states are investigated.
