We review lattice vibrational modes in atomically thin two-dimensional (2D) layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismu...We review lattice vibrational modes in atomically thin two-dimensional (2D) layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between "layers", while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials (MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus), including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories: phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.展开更多
Discovering more and new geometrically frustrated systems remains an active point of inquiry in fundamental physics for the existence of unusual states of matter.Here,we report spin-liquid-like behavior in a two-dimen...Discovering more and new geometrically frustrated systems remains an active point of inquiry in fundamental physics for the existence of unusual states of matter.Here,we report spin-liquid-like behavior in a two-dimensional(2D)rhombic lattice Fe-metal-organic framework(Fe-MOF)with frustrated antiferromagnetism.This Fe-MOF exhibits a high frustration factor f=|θCW|/TN≥315,and its long-range magnetic order is suppressed down to 180 mK.Detailed theoretical calculations demonstrate strong antiferromagnetic coupling between adjacent Fe3+ions,indicating the potential of a classical spin-liquid-like behavior.Notably,a T-linear heat capacity parameter,γ,originating from electronic contributions and with magnetic field independence up to 8 T,can be observed in the specific heat capacity measurements at low-temperature,providing further proof for the spin-liquid-like behavior.This work highlights the potential of MOF materials in geometrically frustrated systems,and will promote the research of exotic quantum physics phenomena.展开更多
摩擦力显微镜(friction force microscopy,FFM)是一种基于摩擦力信号的原子力显微镜,能够对二维材料晶格进行快速、无损的高分辨成像.然而,由于热漂移、黏附力、表面静电等因素的影响,环境条件下二维材料的高分辨FFM成像仍面临着巨大挑...摩擦力显微镜(friction force microscopy,FFM)是一种基于摩擦力信号的原子力显微镜,能够对二维材料晶格进行快速、无损的高分辨成像.然而,由于热漂移、黏附力、表面静电等因素的影响,环境条件下二维材料的高分辨FFM成像仍面临着巨大挑战.基于以上问题,本文以高定向热解石墨为标准样品,通过对探针在样品表面黏滑行为的分析,系统研究了探针弹性常数、正应力和扫描速度对高分辨FFM成像的影响,并建立了一套可靠的二维材料晶格结构表征方法.该方法能够获得精确的结构信息,所测得的二维材料晶格常数平均误差小于2.3%.此外,该方法还适用于化学气相沉积法和剥离法制备的多种二维材料,展现出较高的普适性.本文的研究结果为环境条件下二维材料晶格结构的精确表征提供了新思路.展开更多
Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide ...Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide rich information,such as lattice structure,phonon dispersion,electronic band structure and electron–phonon coupling.Here,we provide a mini review on the lattice vibrations in vdWHs probed by Raman spectroscopy.First,we introduced different kinds of vdWHs,including their structures,properties and potential applications.Second,we discussed interlayer and intralayer phonon in twist multilayer graphene and MoS2.The frequencies of interlayer and intralayer modes can be reproduced by linear chain model(LCM)and phonon folding induced by periodical moiré potentials,respectively.Then,we extended LCM to vdWHs formed by distinct 2D materials,such as MoS2/graphene and hBN/WS2 heterostructures.We further demonstrated how to calculate Raman intensity of interlayer modes in vdWHs by interlayer polarizability model.展开更多
We theoretically demonstrate the imaging properties of a complex two-dimensional(2D) face-centered square lattice photonic crystal(PC) made from germanium cylinders in air background. The finitedifference time-domain(...We theoretically demonstrate the imaging properties of a complex two-dimensional(2D) face-centered square lattice photonic crystal(PC) made from germanium cylinders in air background. The finitedifference time-domain(FDTD) method is employed to calculate the band structure and simulate image construction. The band diagram of the complex structure is significantly compressed. Negative refraction occurs in the second energy band with negative phase velocity at a frequency of 0.228(2πc/a), which is lower than results from previous studies. Lower negative refraction frequency leads to higher image resolution. Numerical results show that the spatial resolution of the system reaches 0.7296λ, which is lower than the incident wavelength.展开更多
Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetMs, and 3D node-line semimetals (NLSs). In particul...Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetMs, and 3D node-line semimetals (NLSs). In particular, several compounds (e.g., certain 3D graphene networks, Cu3PdN, Ca3P2 ) were discovered to be 3D NLSs, in which the conduction and valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional (2D) Dirac semimetal (e.g., graphene), 2D topological semimetals are much less investigated. Here we propose a new concept of a 2D NLS and suggest that this state could be realized in a new mixed lattice (named as HK lattice) composed by Kagome and honeycomb lattices. It is found that A3B2 (A is a group-liB cation and B is a group-VA anion) compounds (such as Hg3As2) with the HK lattice are 2D NLSs due to the band inversion between the cation Hg-s orbital and the anion As-pz orbital with respect to the mirror symmetry. Since the band inversion occurs between two bands with the same parity, this peculiar 2D NLS could be used as transparent conductors. In the presence of buckling or spin-orbit coupling, the 2D NLS state may turn into a 2D Dirac semimetal state or a 2D topological crystalline insulating state. Since the band gap opening due to buckling or spin-orbit coupling is small, Hg3As3 with the HK lattice can still be regarded as a 2D NLS at room temperature. Our work suggests a new route to design topological materials without involving states with opposite parities.展开更多
The discovery of graphene has led to the devotion of intensive efforts,theoretical and experimental,to produce two-dimensional(2D)materials that can be used for developing functional materials and devices.This work pr...The discovery of graphene has led to the devotion of intensive efforts,theoretical and experimental,to produce two-dimensional(2D)materials that can be used for developing functional materials and devices.This work provides a brief review of the recent developments in the lattice models of 2D Dirac materials and their relevant real material counterparts that are crucial for understanding the origins of 2D Dirac cones in electronic band structures as well as their material design and device applications.We focus on the roles of lattice symmetry,atomic orbital hybridization,and spin-orbit coupling in the presence of a Dirac cone.A number of lattice models,such as honeycomb,kagome,ruby,star,Cairo,and line-centered honeycomb,with different symmetries are reviewed based on the tight-binding approach.Inorganic and organic 2D materials,theoretically proposed or experimentally synthesized to satisfy these 2D Dirac lattice models,are summarized.展开更多
Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation,but also is helpful for furthe...Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation,but also is helpful for further understanding the heavy fermion superconductivity.Here we report a low-temperature and vector-magneticfield scanning tunneling microscopy and spectroscopy study on a superconducting compound(4Hb-TaS_(2))with alternate stacking of 1T-TaS_(2)and 1H-TaS_(2)layers.We observe the quasi-two-dimensional superconductivity in the 1H-TaS_(2)layer with anisotropic response to the in-plane and out-of-plane magnetic fields.In the 1T-TaS_(2)layer,we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters.We also find that the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level,and it can be significantly enhanced when it is further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS_(2)surface.Our results not only are important for fully understanding the electronic properties of 4Hb-TaS_(2),but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.展开更多
We restrict our attention to the discrete two-dimensional monatomic β-FPU lattice. We look for two- dimensional breather lattice solutions and two-dimensional compact-like discrete breathers by using trying method an...We restrict our attention to the discrete two-dimensional monatomic β-FPU lattice. We look for two- dimensional breather lattice solutions and two-dimensional compact-like discrete breathers by using trying method and analyze their stability by using Aubry's linearly stable theory. We obtain the conditions of existence and stability of two-dimensional breather lattice solutions and two-dimensional compact-like discrete breathers in the discrete two- dimensional monatomic β-FPU lattice.展开更多
Recently, a new type of second-order topological insulator has been theoretically proposed by introducing an in-plane Zeeman field into the Kane-Mele model in the two-dimensional honeycomb lattice. A pair of topologic...Recently, a new type of second-order topological insulator has been theoretically proposed by introducing an in-plane Zeeman field into the Kane-Mele model in the two-dimensional honeycomb lattice. A pair of topological corner states arise at the corners with obtuse angles of an isolated diamond-shaped flake. To probe the corner states, we study their transport properties by attaching two leads to the system. Dressed by incoming electrons, the dynamic corner state is very different from its static counterpart.Resonant tunneling through the dressed corner state can occur by tuning the in-plane Zeeman field. At the resonance, the pair of spatially well separated and highly localized corner states can form a dimer state, whose wavefunction extends almost the entire bulk of the diamond-shaped flake. By varying the Zeeman field strength, multiple resonant tunneling events are mediated by the same dimer state. This re-entrance effect can be understood by a simple model. These findings extend our understanding of dynamic aspects of the second-order topological corner states.展开更多
To date, a number of two-dimensional (2D) topological insulators (TIs) have been realized in Group 14 elemental honeycomb lattices, but all are inversionsymmetric. Here, based on first-principles calculations, we ...To date, a number of two-dimensional (2D) topological insulators (TIs) have been realized in Group 14 elemental honeycomb lattices, but all are inversionsymmetric. Here, based on first-principles calculations, we predict a new family of 2D inversion-asymmetric TIs with sizeable bulk gaps from 105 meV to 284 meV, in X2-GeSn (X = H, F, Cl, Br, I) monolayers, making them in principle suitable for room-temperature applications. The nontrivial topological characteristics of inverted band orders are identified in pristine X2-GeSn with X = (F, Cl, Br, I), whereas H2-GeSn undergoes a nontrivial band inversion at 8% lattice expansion. Topologically protected edge states are identified in X2-GeSn with X = (F, Cl, Br, I), as well as in strained H2-GeSn. More importantly, the edges of these systems, which exhibit single-Dirac-cone characteristics located exactly in the middle of their bulk band gaps, are ideal for dissipationless transport. Thus, Group 14 elemental honeycomb lattices provide a fascinating playground for the manipulation of quantum states.展开更多
A two-dimensional coupled model of the cellular automaton(CA)and the lattice Boltzmann method(LBM)was developed to simulate the solute dendrite growth of Fe-C-Mn-S alloy in the presence of forced convection.The model ...A two-dimensional coupled model of the cellular automaton(CA)and the lattice Boltzmann method(LBM)was developed to simulate the solute dendrite growth of Fe-C-Mn-S alloy in the presence of forced convection.The model describes the transport phenomenon by the evolution of moving pseudo-particles distribution functions and utilizes the LBM to solve fluid flow and solute transport under forced convection numerically.Based on the solute field calculated by the CA technique,the dynamics of dendrite growth were determined by the previously proposed local solute balance method.The accuracy of the forced convection dendrite growth model was verified by comparing the CA-LBM model with Lipton-Glicksman-Kurz analytical model.It is revealed that the dendrite symmetry structure is destroyed compared to free diffusion,and the upstream arm is more developed than the downstream arm of the dendrite.The enriched solute segregates more at the downstream side than at the upstream side of the dendrite.The length of the upstream dendrite arm increases firstly and then becomes stable with the increase in the flow velocity,the dendrite necking is restrained,and the vertical dendrite arm becomes longer.展开更多
A quantum-spin-Hall (QSH) state was achieved experimentally, albeit at a low critical temperature because of the narrow band gap of the bulk material. Two- dimensional topological insulators are critically important...A quantum-spin-Hall (QSH) state was achieved experimentally, albeit at a low critical temperature because of the narrow band gap of the bulk material. Two- dimensional topological insulators are critically important for realizing novel topological applications. Using density functional theory (DFT), we demonstrated that hydrogenated GaBi bilayers (HGaBi) form a stable topological insulator with a large nontrivial band gap of 0.320 eV, based on the state-of-the-art hybrid functional method, which is implementable for achieving QSH states at room temperature. The nontrivial topological property of the HGaBi lattice can also be confirmed from the appearance of gapless edge states in the nanoribbon structure. Our results provide a versatile platform for hosting nontrivial topological states usable for important nanoelectronic device applications.展开更多
基金Q. H. X. gratefully thanks Singapore National Research Foundation via a Fellowship grant (No. NRF-RF2009-06) and an Investigatorship grant (No. NRF-NRFI2015-03), Ministry of Education via a tier2 grant (No. MOE2012-T2-2-086) and a tier1 grant (No. 2013-T1-002-232). S. Y. Q. and X. Luo gratefully acknowledge the Singapore National Research Foun- dation (NRF) for funding under the NRF Fellowship (No. NRF-NRFF2013-07). Z. J. gratefully thanks National Natural Science Foundation of China (Nos. 11574305 and 51527901) and financial support from the National 1000 Talent Plan of China via a Young Project. The computations were performed on the cluster of NUS Graphene Research Centre. S. Y. Q. and X. Luo acknowledge the National Research Foundation, Prime Minister's Office, Singapore, under its Medium Sized Centre Programme.
文摘We review lattice vibrational modes in atomically thin two-dimensional (2D) layered materials, focusing on 2D materials beyond graphene, such as group VI transition metal dichalcogenides, topological insulator bismuth chalcogenides, and black phosphorus. Although the composition and structure of those materials are remarkably different, they share a common and important feature, i.e., their bulk crystals are stacked via van der Waals interactions between "layers", while each layer is comprised of one or more atomic planes. First, we review the background of some 2D materials (MX2, M = Mo, W; X = S, Se, Te. Bi2X3, X = Se, Te. Black phosphorus), including crystalline structures and stacking order. We then review the studies on vibrational modes of layered materials and nanostructures probed by the powerful yet nondestructive Raman spectroscopy technique. Based on studies conducted before 2010, recent investigations using more advanced techniques have pushed the studies of phonon modes in 2D layered materials to the atomically thin regime, down to monolayers. We will classify the recently reported general features into the following categories: phonon confinement effects and electron-phonon coupling, anomalous shifts in high-frequency intralayer vibrational modes and surface effects, reduced dimensionality and lower symmetry, the linear chain model and the substrate effect, stacking orders and interlayer shear modes, polarization dependence, and the resonance effect. Within the seven categories, both intralayer and interlayer vibrational modes will be discussed. The comparison between different materials will be provided as well.
基金supported by the National Key Research and Development Program of China(No.2021YFA1600800)the National Natural Science Foundation of China(Nos.11975234,12075243,12005227,12105286,121350122,U2032150,12275271,12205305,and U1932211)+5 种基金the Natural Science Foundation of Anhui Province(Nos.2208085QA14 and 2208085J13)the Users with Excellence Program of Hefei Science Center CAS(Nos.2020HSC-UE002,2020HSC-CIP013,2021HSC-UE002,and 2021HSC-UE003)the Major science and technology project of Anhui Province(No.202103a05020025)the Key Program of Research and Development of Hefei Science Center,CAS(Nos.2021HSC-KPRD002 and 2021HSC-KPRD003)the Fundamental Research Funds for the Central Universities(No.WK 2310000103)partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication.
文摘Discovering more and new geometrically frustrated systems remains an active point of inquiry in fundamental physics for the existence of unusual states of matter.Here,we report spin-liquid-like behavior in a two-dimensional(2D)rhombic lattice Fe-metal-organic framework(Fe-MOF)with frustrated antiferromagnetism.This Fe-MOF exhibits a high frustration factor f=|θCW|/TN≥315,and its long-range magnetic order is suppressed down to 180 mK.Detailed theoretical calculations demonstrate strong antiferromagnetic coupling between adjacent Fe3+ions,indicating the potential of a classical spin-liquid-like behavior.Notably,a T-linear heat capacity parameter,γ,originating from electronic contributions and with magnetic field independence up to 8 T,can be observed in the specific heat capacity measurements at low-temperature,providing further proof for the spin-liquid-like behavior.This work highlights the potential of MOF materials in geometrically frustrated systems,and will promote the research of exotic quantum physics phenomena.
文摘摩擦力显微镜(friction force microscopy,FFM)是一种基于摩擦力信号的原子力显微镜,能够对二维材料晶格进行快速、无损的高分辨成像.然而,由于热漂移、黏附力、表面静电等因素的影响,环境条件下二维材料的高分辨FFM成像仍面临着巨大挑战.基于以上问题,本文以高定向热解石墨为标准样品,通过对探针在样品表面黏滑行为的分析,系统研究了探针弹性常数、正应力和扫描速度对高分辨FFM成像的影响,并建立了一套可靠的二维材料晶格结构表征方法.该方法能够获得精确的结构信息,所测得的二维材料晶格常数平均误差小于2.3%.此外,该方法还适用于化学气相沉积法和剥离法制备的多种二维材料,展现出较高的普适性.本文的研究结果为环境条件下二维材料晶格结构的精确表征提供了新思路.
基金the National Key Research and Development Program of China (Grant No.2016YFA0301204)the National Natural Science Foundation of China (Grant Nos.11874350 and 11434010)
文摘Research on two-dimensional(2D) materials and related van der Waals heterostructures(vdWHs) is intense and remains one of the leading topics in condensed matter physics.Lattice vibrations or phonons of a vdWH provide rich information,such as lattice structure,phonon dispersion,electronic band structure and electron–phonon coupling.Here,we provide a mini review on the lattice vibrations in vdWHs probed by Raman spectroscopy.First,we introduced different kinds of vdWHs,including their structures,properties and potential applications.Second,we discussed interlayer and intralayer phonon in twist multilayer graphene and MoS2.The frequencies of interlayer and intralayer modes can be reproduced by linear chain model(LCM)and phonon folding induced by periodical moiré potentials,respectively.Then,we extended LCM to vdWHs formed by distinct 2D materials,such as MoS2/graphene and hBN/WS2 heterostructures.We further demonstrated how to calculate Raman intensity of interlayer modes in vdWHs by interlayer polarizability model.
文摘We theoretically demonstrate the imaging properties of a complex two-dimensional(2D) face-centered square lattice photonic crystal(PC) made from germanium cylinders in air background. The finitedifference time-domain(FDTD) method is employed to calculate the band structure and simulate image construction. The band diagram of the complex structure is significantly compressed. Negative refraction occurs in the second energy band with negative phase velocity at a frequency of 0.228(2πc/a), which is lower than results from previous studies. Lower negative refraction frequency leads to higher image resolution. Numerical results show that the spatial resolution of the system reaches 0.7296λ, which is lower than the incident wavelength.
基金Supported by the National Natural Science Foundation of China under Grant No 11374056the Special Funds for Major State Basic Research under Grant No 2015CB921700+1 种基金the Program for Professor of Special Appointment(Eastern Scholar)the Qing Nian Ba Jian Program,and the Fok Ying Tung Education Foundation
文摘Recently, the concept of topological insulators has been generalized to topological semimetals, including three-dimensional (3D) Weyl semimetals, 3D Dirac semimetMs, and 3D node-line semimetals (NLSs). In particular, several compounds (e.g., certain 3D graphene networks, Cu3PdN, Ca3P2 ) were discovered to be 3D NLSs, in which the conduction and valence bands cross at closed lines in the Brillouin zone. Except for the two-dimensional (2D) Dirac semimetal (e.g., graphene), 2D topological semimetals are much less investigated. Here we propose a new concept of a 2D NLS and suggest that this state could be realized in a new mixed lattice (named as HK lattice) composed by Kagome and honeycomb lattices. It is found that A3B2 (A is a group-liB cation and B is a group-VA anion) compounds (such as Hg3As2) with the HK lattice are 2D NLSs due to the band inversion between the cation Hg-s orbital and the anion As-pz orbital with respect to the mirror symmetry. Since the band inversion occurs between two bands with the same parity, this peculiar 2D NLS could be used as transparent conductors. In the presence of buckling or spin-orbit coupling, the 2D NLS state may turn into a 2D Dirac semimetal state or a 2D topological crystalline insulating state. Since the band gap opening due to buckling or spin-orbit coupling is small, Hg3As3 with the HK lattice can still be regarded as a 2D NLS at room temperature. Our work suggests a new route to design topological materials without involving states with opposite parities.
基金the National Natural Science Founda-tion of China(No.12074215)and Taishan Scholar Program of Shandong Province.
文摘The discovery of graphene has led to the devotion of intensive efforts,theoretical and experimental,to produce two-dimensional(2D)materials that can be used for developing functional materials and devices.This work provides a brief review of the recent developments in the lattice models of 2D Dirac materials and their relevant real material counterparts that are crucial for understanding the origins of 2D Dirac cones in electronic band structures as well as their material design and device applications.We focus on the roles of lattice symmetry,atomic orbital hybridization,and spin-orbit coupling in the presence of a Dirac cone.A number of lattice models,such as honeycomb,kagome,ruby,star,Cairo,and line-centered honeycomb,with different symmetries are reviewed based on the tight-binding approach.Inorganic and organic 2D materials,theoretically proposed or experimentally synthesized to satisfy these 2D Dirac lattice models,are summarized.
基金the financial support from the National Key R&D Program of China(Grant No.2020YFA0309602)the National Natural Science Foundation of China(Grant No.11874042)+7 种基金the support from National Natural Science Foundation of China(Grant No.12004250)the support from the National Natural Science Foundation of China(Grant No.12004251)the National Natural Science Foundation of China(Grant Nos.11674326 and 11774351)the start-up funding from Shanghai Tech Universitythe Shanghai Sailing Program(Grant No.20YF1430700)the Shanghai Sailing Program(Grant No.21YF1429200)the support from the National Key R&D Program(Grant No.2021YFA1600201)the Joint Funds of the National Natural Science Foundation of China and the Chinese Academy of Sciences’Large-Scale Scientific Facility(Grant Nos.U1832141,U1932217 and U2032215)。
文摘Realization of Kondo lattice in superconducting van der Waals materials not only provides a unique opportunity for tuning the Kondo lattice behavior by electrical gating or intercalation,but also is helpful for further understanding the heavy fermion superconductivity.Here we report a low-temperature and vector-magneticfield scanning tunneling microscopy and spectroscopy study on a superconducting compound(4Hb-TaS_(2))with alternate stacking of 1T-TaS_(2)and 1H-TaS_(2)layers.We observe the quasi-two-dimensional superconductivity in the 1H-TaS_(2)layer with anisotropic response to the in-plane and out-of-plane magnetic fields.In the 1T-TaS_(2)layer,we detect the Kondo resonance peak that results from the Kondo screening of the unpaired electrons in the Star-of-David clusters.We also find that the intensity of the Kondo resonance peak is sensitive to its relative position with the Fermi level,and it can be significantly enhanced when it is further shifted towards the Fermi level by evaporating Pb atoms onto the 1T-TaS_(2)surface.Our results not only are important for fully understanding the electronic properties of 4Hb-TaS_(2),but also pave the way for creating tunable Kondo lattice in the superconducting van der Waals materials.
基金supported by National Natural Science Foundation of China under Grant No. 1057400the Natural Science Foundation of Heilongjiang Province under Grant No. A200506
文摘We restrict our attention to the discrete two-dimensional monatomic β-FPU lattice. We look for two- dimensional breather lattice solutions and two-dimensional compact-like discrete breathers by using trying method and analyze their stability by using Aubry's linearly stable theory. We obtain the conditions of existence and stability of two-dimensional breather lattice solutions and two-dimensional compact-like discrete breathers in the discrete two- dimensional monatomic β-FPU lattice.
基金supported by the National Natural Science Foundation of China(Grant No.12034014)the Natural Science Foundation of Guangdong Province(Grant No.2020A1515011418)the Natural Science Foundation of Shenzhen(Grant Nos.JCYJ20190808152801642,and JCYJ20190808150409413)。
文摘Recently, a new type of second-order topological insulator has been theoretically proposed by introducing an in-plane Zeeman field into the Kane-Mele model in the two-dimensional honeycomb lattice. A pair of topological corner states arise at the corners with obtuse angles of an isolated diamond-shaped flake. To probe the corner states, we study their transport properties by attaching two leads to the system. Dressed by incoming electrons, the dynamic corner state is very different from its static counterpart.Resonant tunneling through the dressed corner state can occur by tuning the in-plane Zeeman field. At the resonance, the pair of spatially well separated and highly localized corner states can form a dimer state, whose wavefunction extends almost the entire bulk of the diamond-shaped flake. By varying the Zeeman field strength, multiple resonant tunneling events are mediated by the same dimer state. This re-entrance effect can be understood by a simple model. These findings extend our understanding of dynamic aspects of the second-order topological corner states.
文摘To date, a number of two-dimensional (2D) topological insulators (TIs) have been realized in Group 14 elemental honeycomb lattices, but all are inversionsymmetric. Here, based on first-principles calculations, we predict a new family of 2D inversion-asymmetric TIs with sizeable bulk gaps from 105 meV to 284 meV, in X2-GeSn (X = H, F, Cl, Br, I) monolayers, making them in principle suitable for room-temperature applications. The nontrivial topological characteristics of inverted band orders are identified in pristine X2-GeSn with X = (F, Cl, Br, I), whereas H2-GeSn undergoes a nontrivial band inversion at 8% lattice expansion. Topologically protected edge states are identified in X2-GeSn with X = (F, Cl, Br, I), as well as in strained H2-GeSn. More importantly, the edges of these systems, which exhibit single-Dirac-cone characteristics located exactly in the middle of their bulk band gaps, are ideal for dissipationless transport. Thus, Group 14 elemental honeycomb lattices provide a fascinating playground for the manipulation of quantum states.
基金funded by the National Natural Science Foundation of China(Grant Nos.52074071 and U1660204)Fundamental Research Funds for the Central Universities of China(Grant No.N172502006)Liaoning Revitalization Talents Program(Grant No.XLYC1802032).
文摘A two-dimensional coupled model of the cellular automaton(CA)and the lattice Boltzmann method(LBM)was developed to simulate the solute dendrite growth of Fe-C-Mn-S alloy in the presence of forced convection.The model describes the transport phenomenon by the evolution of moving pseudo-particles distribution functions and utilizes the LBM to solve fluid flow and solute transport under forced convection numerically.Based on the solute field calculated by the CA technique,the dynamics of dendrite growth were determined by the previously proposed local solute balance method.The accuracy of the forced convection dendrite growth model was verified by comparing the CA-LBM model with Lipton-Glicksman-Kurz analytical model.It is revealed that the dendrite symmetry structure is destroyed compared to free diffusion,and the upstream arm is more developed than the downstream arm of the dendrite.The enriched solute segregates more at the downstream side than at the upstream side of the dendrite.The length of the upstream dendrite arm increases firstly and then becomes stable with the increase in the flow velocity,the dendrite necking is restrained,and the vertical dendrite arm becomes longer.
文摘A quantum-spin-Hall (QSH) state was achieved experimentally, albeit at a low critical temperature because of the narrow band gap of the bulk material. Two- dimensional topological insulators are critically important for realizing novel topological applications. Using density functional theory (DFT), we demonstrated that hydrogenated GaBi bilayers (HGaBi) form a stable topological insulator with a large nontrivial band gap of 0.320 eV, based on the state-of-the-art hybrid functional method, which is implementable for achieving QSH states at room temperature. The nontrivial topological property of the HGaBi lattice can also be confirmed from the appearance of gapless edge states in the nanoribbon structure. Our results provide a versatile platform for hosting nontrivial topological states usable for important nanoelectronic device applications.