The risk of flammability is an unavoidable issue for gel polymer electrolytes(GPEs).Usually,flameretardant solvents are necessary to be used,but most of them would react with anode/cathode easily and cause serious int...The risk of flammability is an unavoidable issue for gel polymer electrolytes(GPEs).Usually,flameretardant solvents are necessary to be used,but most of them would react with anode/cathode easily and cause serious interfacial instability,which is a big challenge for design and application of nonflammable GPEs.Here,a nonflammable GPE(SGPE)is developed by in situ polymerizing trifluoroethyl methacrylate(TFMA)monomers with flame-retardant triethyl phosphate(TEP)solvents and LiTFSI–LiDFOB dual lithium salts.TEP is strongly anchored to PTFMA matrix via polarity interaction between-P=O and-CH_(2)CF_(3).It reduces free TEP molecules,which obviously mitigates interfacial reactions,and enhances flame-retardant performance of TEP surprisingly.Anchored TEP molecules are also inhibited in solvation of Li^(+),leading to anion-dominated solvation sheath,which creates inorganic-rich solid electrolyte interface/cathode electrolyte interface layers.Such coordination structure changes Li^(+)transport from sluggish vehicular to fast structural transport,raising ionic conductivity to 1.03 mS cm^(-1) and transfer number to 0.41 at 30℃.The Li|SGPE|Li cell presents highly reversible Li stripping/plating performance for over 1000 h at 0.1 mA cm^(−2),and 4.2 V LiCoO_(2)|SGPE|Li battery delivers high average specific capacity>120 mAh g^(−1) over 200 cycles.This study paves a new way to make nonflammable GPE that is compatible with Li metal anode.展开更多
Harmonic thermoelastic waves in helical strands with Maxwell–Cattaneo heat conduction areinvestigated analytically and numerically. The corresponding dispersion relation is a sixth-orderalgebraic equation, governed b...Harmonic thermoelastic waves in helical strands with Maxwell–Cattaneo heat conduction areinvestigated analytically and numerically. The corresponding dispersion relation is a sixth-orderalgebraic equation, governed by six non-dimensional parameters: two thermoelastic couplingconstants, one chirality parameter, the ratio between extensional and torsional moduli, the Fouriernumber, and the dimensionless thermal relaxation. The behavior of the solutions is discussedfrom two perspectives with an asymptotic-numerical approach: (1) the effect of thermal relaxationon the elastic wave celerities, and (2) the effect of thermoelastic coupling on the thermal wavecelerities. With small wavenumbers, the adiabatic solution for Fourier helical strands is recovered.However, with large wavenumbers, the solutions behave differently depending on the thermalrelaxation and chirality. Due to thermoelastic coupling, the thermal wave celerity deviates from theclassical result of the speed of second sound.展开更多
Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensedmatter.However,the onlyway to determine crystal structures of ma...Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensedmatter.However,the onlyway to determine crystal structures of materials above 100 GPa,namely,X-ray diffraction(XRD),especially for lowZ materials,remains nontrivial in the ultrahigh-pressure region,even with the availability of brilliant synchrotron X-ray sources.In thiswork,we performa systematic study,choosing hydrogen(the lowest X-ray scatterer)as the subject,to understand how to better perform XRD measurements of low Z materials at multimegabar pressures.The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254GPa at room temperature[C.Ji et al.,Nature 573,558–562(2019)].Wepresent our discoveries and experienceswith regard to several aspects of thiswork,namely,diamond anvil selection,sample configuration for ultrahigh-pressure XRDstudies,XRDdiagnostics for low Z materials,and related issues in data interpretation and pressure calibration.Webelieve that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures,eventually testing structural models of metallic hydrogen.展开更多
In this paper, considering the Hirota and the Maxwell–Bloch （H-MB） equations which are governed by femtosecond pulse propagation through a two-level doped fiber system, we construct the Darboux transformation of th...In this paper, considering the Hirota and the Maxwell–Bloch （H-MB） equations which are governed by femtosecond pulse propagation through a two-level doped fiber system, we construct the Darboux transformation of this system through a linear eigenvalue problem. Using this Daurboux transformation, we generate multi-soliton, positon, and breather solutions （both bright and dark breathers） of the H-MB equations. Finally, we also construct the rogue wave solutions of the above system.展开更多
We present the spin polarized calculations on the new Zr2NiX (X = Al, Ga) alloys. Band structure analysis present them as half-metallic compounds with integral spin magnetic moment of 3 B following the general Slater-...We present the spin polarized calculations on the new Zr2NiX (X = Al, Ga) alloys. Band structure analysis present them as half-metallic compounds with integral spin magnetic moment of 3 B following the general Slater-Pauling rule. Thermal effects on some macroscopic properties using quasi-harmonic Debye model which considers the phononic effects, the effects of pressure and temperature are taken into account. The variations of the thermal expansion coefficient, Debye temperature, Gruneisen parameter and heat capacity for the compounds have been investigated for the first time. These thermodynamic properties may prove as a reference for their synthesis.展开更多
Hopf insulators are intriguing three-dimensional topological insulators characterized by an integer topological invariant. They originate from the mathematical theory of Hopf fibration and epitomize the deep connectio...Hopf insulators are intriguing three-dimensional topological insulators characterized by an integer topological invariant. They originate from the mathematical theory of Hopf fibration and epitomize the deep connection between knot theory and topological phases of matter, which distinguishes them from other classes of topological insulators. Here, we implement a model Hamiltonian for Hopf insulators in a solid-state quantum simulator and report the first experimental observation of their topological properties, including nontrivial topological links associated with the Hopf fibration and the integer-valued topological invariant obtained from a direct tomographic measurement. Our observation of topological links and Hopf fibration in a quantum simulator opens the door to probe rich topological properties of Hopf insulators in experiments. The quantum simulation and probing methods are also applicable to the study of other intricate three-dimensional topological model Hamiltonians.展开更多
We have shown here the results of PFEC(photofield emission current)calculated for GaAs(gallium arsenide).We have used the initial state wavefunctions derived using the Kronig-Penney potential model for evaluating the ...We have shown here the results of PFEC(photofield emission current)calculated for GaAs(gallium arsenide).We have used the initial state wavefunctions derived using the Kronig-Penney potential model for evaluating the PFEC.We have found that PFEC is not oscillatory as obtained by Modinos and Klient,[Solid State Commun.50,651(1984)],but it is an exponential function.展开更多
In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials(MMs) at will. We give three examples of metamaterial designs th...In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials(MMs) at will. We give three examples of metamaterial designs that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numerical simulations. Particular emphasis is put on the significance of such tailored effective properties of optical MMs.展开更多
Knots and links are fascinating and intricate topological objects.Their influence spans from DNA and molecular chemistry to vortices in superfluid helium,defects in liquid crystals and cosmic strings in the early univ...Knots and links are fascinating and intricate topological objects.Their influence spans from DNA and molecular chemistry to vortices in superfluid helium,defects in liquid crystals and cosmic strings in the early universe.Here we find that knotted structures also exist in a peculiar class of three-dimensional topological insulators—the Hopf insulators.In particular,we demonstrate that the momentum-space spin textures of Hopf insulators are twisted in a nontrivial way,which implies the presence of various knot and link structures.We further illustrate that the knots and nontrivial spin textures can be probed via standard time-of-flight images in cold atoms as preimage contours of spin orientations in stereographic coordinates.The extracted Hopf invariants,knots,and links are validated to be robust to typical experimental imperfections.Our work establishes the existence of knotted structures in Hopf insulators,which may have potential applications in spintronics and quantum information processing.展开更多
The rise of automation and machine learning(ML)in electron microscopy has the potential to revolutionize materials research through autonomous data collection and processing.A significant challenge lies in developing ...The rise of automation and machine learning(ML)in electron microscopy has the potential to revolutionize materials research through autonomous data collection and processing.A significant challenge lies in developing ML models that rapidly generalize to large data sets under varying experimental conditions.We address this by employing a cycle generative adversarial network(CycleGAN)with a reciprocal space discriminator,which augments simulated data with realistic spatial frequency information.This allows the CycleGAN to generate images nearly indistinguishable from real data and provide labels for ML applications.We showcase our approach by training a fully convolutional network(FCN)to identify single atom defects in a 4.5 million atom data set,collected using automated acquisition in an aberration-corrected scanning transmission electron microscope(STEM).Our method produces adaptable FCNs that can adjust to dynamically changing experimental variables with minimal intervention,marking a crucial step towards fully autonomous harnessing of microscopy big data.展开更多
Moirésuperlattices of transition metal dichalcogenide(TMD)heterostructures give rise to rich excitonic phenomena associated with the interlayer twist angle.Theoretical calculations of excitons in such systems are...Moirésuperlattices of transition metal dichalcogenide(TMD)heterostructures give rise to rich excitonic phenomena associated with the interlayer twist angle.Theoretical calculations of excitons in such systems are typically based on model moirépotentials that mitigate the computational cost.However,predictive understanding of the electron-hole coupling dominating the excitations is crucial to realize the twist-induced modifications of the optical selection rules.In this work,we use many-body perturbation theory to evaluate the relation between twist angle and exciton properties in TMD heterostructures.We present an approach for unfolding excitonic states from the moiréBrillouin zone onto the separate-layer ones.Applying this method to a large-angle twisted MoS^(2)/MoSe^(2) bilayer,we find that the optical spectrum is dominated by mixed electron–hole transitions with different momenta in the separate monolayers,leading to unexpected hybridization between interlayer and intralayer excitons.Our findings offer a design pathway for exciton layer-localization in TMD heterostructures.展开更多
In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron＇s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 （P212121 ）...In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron＇s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 （P212121 ） and No. 198 （P213）, which have three orthogonal screw rotation axes. In the case of space groups No. 61 （Pbca） and No. 205 （Pa-3） that have extra inversion symmetry, Weyl points are promoted to four-fold degenerate line nodes in glide-invariant planes. The three-fold rotation symmetry present in the space groups No. 198 and No. 205 allows Weyl and Dirac points, respectively, to appear along its rotation axes in the Brillouin zone and generates four-fold and six-fold degeneracy at the F point and R point, respectively.展开更多
In recent years,femtosecond(fs)-lasers have evolved into a versatile tool for high precision micromachining of transparent materials because nonlinear absorption in the focus can result in refractive index modificatio...In recent years,femtosecond(fs)-lasers have evolved into a versatile tool for high precision micromachining of transparent materials because nonlinear absorption in the focus can result in refractive index modifications or material disruptions.However,when high pulse energies or low numerical apertures are required,nonlinear side effects such as self-focusing,filamentation or white light generation can decrease the modification quality.In this paper,we apply simultaneous spatial and temporal focusing(SSTF)to overcome these limitations.The main advantage of SSTF is that the ultrashort pulse is only formed at the focal plane,thereby confining the intensity distribution strongly to the focal volume and suppressing detrimental nonlinear side effects.Thus,we investigate the optical breakdown within a water cell by pump-probe shadowgraphy,comparing conventional focusing and SSTF under equivalent focusing conditions.The plasma formation is well confined for low pulse energies,2 mJ,but higher pulse energies lead to the filamentation and break-up of the disruptions for conventional focusing,thereby decreasing the modification quality.In contrast,plasma induced by SSTF stays well confined to the focal plane,even for high pulse energies up to 8 mJ,preventing extended filaments,side branches or break-up of the disruptions.Furthermore,while conventional focusing leads to broadband supercontinuum generation,only marginal spectral broadening is observed using SSTF.These experimental findings are in excellent agreement with numerical simulations of the nonlinear pulse propagation and interaction processes.Therefore,SSTF appears to be a powerful tool to control the processing of transparent materials,e.g.,for precise ophthalmic fs-surgery.展开更多
A planar honeycomb monolayer of siligraphene （SIC7） could be a prospective medium for clean energy storage due to its light weight, and its remarkable mechanical and unique electronic properties. By employing van de...A planar honeycomb monolayer of siligraphene （SIC7） could be a prospective medium for clean energy storage due to its light weight, and its remarkable mechanical and unique electronic properties. By employing van der Waals- induced first principles calculations based on density functional theory （DFT）, we have explored the structural, electronic, and hydrogen （H2） storage characteristics of SiC7 sheets decorated with various light metals. The binding energies of lithium （Li）, sodium （Na）, potassium （K）, magnesium （Mg）, calcium （Ca）, scandium （Sc）, and titanium （Ti） dopants on a SiC7 monolayer were studied at various doping concentrations, and found to be strong enough to counteract the metal clustering effect. We further verified the stabilities of the metallized SiC7 sheets at room temperature using ab initio molecular dynamics （MD） simulations. Bader charge analysis revealed that upon adsorption, due to the difference in electronegativity, all the metal adatorns donated a fraction of their electronic charges to the SiC7 sheet. Each partially charged metal center on the SiC7 sheets could bind a maximum of 4 to 5 H2 molecules. A high H2 gravimetric density was achieved for several dopants at a doping concentration of 12.50%. The H2 binding energies were found to fall within the ideal range of 0.2-0.6 eV. Based on these findings, we propose that metal-doped SiC7 sheets can operate as efficient H2 storage media under ambient conditions.展开更多
Recent years have witnessed tremendous success in the discovery of topological states of matter.Particularly,sophisticated theoretical methods in time-reversal-invariant topological phases have been developed,leading ...Recent years have witnessed tremendous success in the discovery of topological states of matter.Particularly,sophisticated theoretical methods in time-reversal-invariant topological phases have been developed,leading to the comprehensive search of crystal database and the prediction of thousands of topological materials.In contrast,the discovery of magnetic topological phases that break time reversal is still limited to several exemplary materials because the coexistence of magnetism and topological electronic band structure is rare in a single compound.To overcome this challenge,we propose an alternative approach to realize the quantum anomalous Hall(QAH)effect,a typical example of magnetic topological phase,via engineering two-dimensional(2D)magnetic van der Waals heterojunctions.展开更多
The structural, dynamical, and electronic properties of compressed Sr C2 were systematically investigated up to 200 GPa by using ab initio method. Three new phases are obtained by means of evolutionary algorithm. The ...The structural, dynamical, and electronic properties of compressed Sr C2 were systematically investigated up to 200 GPa by using ab initio method. Three new phases are obtained by means of evolutionary algorithm. The confirmed most stable structure has C2/c symmetry at zero pressure, which transforms into an orthorhombic Cmcm phase at 4.5 GPa, followed by another orthorhombic Immm phase, which is stabilized at wide pressure range of 21.5–123.5 GPa, and then transformed into Mg B2-type phase(space group, P6/mmm). Although Sr C2 has similar structural transformation to that of compressed Ca C2, Sr C2 holds small electron–phonon coupling,which leads to its low superconducting critical temperature(only 1.8 K).展开更多
基金supported by the National Natural Science Foundation of China(Nos.52172214,52272221,52171182)the Postdoctoral Innovation Project of Shandong Province(No.202102003)+2 种基金The Key Research and Development Program of Shandong Province(2021ZLGX01)the Qilu Young Scholar ProgramHPC Cloud Platform of Shandong University are also thanked.
文摘The risk of flammability is an unavoidable issue for gel polymer electrolytes(GPEs).Usually,flameretardant solvents are necessary to be used,but most of them would react with anode/cathode easily and cause serious interfacial instability,which is a big challenge for design and application of nonflammable GPEs.Here,a nonflammable GPE(SGPE)is developed by in situ polymerizing trifluoroethyl methacrylate(TFMA)monomers with flame-retardant triethyl phosphate(TEP)solvents and LiTFSI–LiDFOB dual lithium salts.TEP is strongly anchored to PTFMA matrix via polarity interaction between-P=O and-CH_(2)CF_(3).It reduces free TEP molecules,which obviously mitigates interfacial reactions,and enhances flame-retardant performance of TEP surprisingly.Anchored TEP molecules are also inhibited in solvation of Li^(+),leading to anion-dominated solvation sheath,which creates inorganic-rich solid electrolyte interface/cathode electrolyte interface layers.Such coordination structure changes Li^(+)transport from sluggish vehicular to fast structural transport,raising ionic conductivity to 1.03 mS cm^(-1) and transfer number to 0.41 at 30℃.The Li|SGPE|Li cell presents highly reversible Li stripping/plating performance for over 1000 h at 0.1 mA cm^(−2),and 4.2 V LiCoO_(2)|SGPE|Li battery delivers high average specific capacity>120 mAh g^(−1) over 200 cycles.This study paves a new way to make nonflammable GPE that is compatible with Li metal anode.
基金supported by the National Science Foundation of United States (Grants IIP-1362146 and CMMI-1462749)
文摘Harmonic thermoelastic waves in helical strands with Maxwell–Cattaneo heat conduction areinvestigated analytically and numerically. The corresponding dispersion relation is a sixth-orderalgebraic equation, governed by six non-dimensional parameters: two thermoelastic couplingconstants, one chirality parameter, the ratio between extensional and torsional moduli, the Fouriernumber, and the dimensionless thermal relaxation. The behavior of the solutions is discussedfrom two perspectives with an asymptotic-numerical approach: (1) the effect of thermal relaxationon the elastic wave celerities, and (2) the effect of thermoelastic coupling on the thermal wavecelerities. With small wavenumbers, the adiabatic solution for Fourier helical strands is recovered.However, with large wavenumbers, the solutions behave differently depending on the thermalrelaxation and chirality. Due to thermoelastic coupling, the thermal wave celerity deviates from theclassical result of the speed of second sound.
基金This research was supported by the National Natural Science Foundation of China under Award No.U1930401the Department of Energy(DOE),Office of Basic Energy Science,Division of Materials Sciences and Engineering under Award No.DE-FG02-99ER45775
文摘Diamond anvil cell techniques have been improved to allow access to the multimegabar ultrahigh-pressure region for exploring novel phenomena in condensedmatter.However,the onlyway to determine crystal structures of materials above 100 GPa,namely,X-ray diffraction(XRD),especially for lowZ materials,remains nontrivial in the ultrahigh-pressure region,even with the availability of brilliant synchrotron X-ray sources.In thiswork,we performa systematic study,choosing hydrogen(the lowest X-ray scatterer)as the subject,to understand how to better perform XRD measurements of low Z materials at multimegabar pressures.The techniques that we have developed have been proved to be effective in measuring the crystal structure of solid hydrogen up to 254GPa at room temperature[C.Ji et al.,Nature 573,558–562(2019)].Wepresent our discoveries and experienceswith regard to several aspects of thiswork,namely,diamond anvil selection,sample configuration for ultrahigh-pressure XRDstudies,XRDdiagnostics for low Z materials,and related issues in data interpretation and pressure calibration.Webelieve that these methods can be readily extended to other low Z materials and can pave the way for studying the crystal structure of hydrogen at higher pressures,eventually testing structural models of metallic hydrogen.
基金Project supported by the Natural Science Foundation of Zhejiang Province of China (Grant No. LY12A01007)the National Natural Science Foundation of China (Grant Nos. 11201251, 10971109, and 11271210)+1 种基金K. C. Wong Magna Fund in Ningbo Universitythe DST,DAE-BRNS, UGC, and CSIR, Government of India, for the financial support through major projects
文摘In this paper, considering the Hirota and the Maxwell–Bloch （H-MB） equations which are governed by femtosecond pulse propagation through a two-level doped fiber system, we construct the Darboux transformation of this system through a linear eigenvalue problem. Using this Daurboux transformation, we generate multi-soliton, positon, and breather solutions （both bright and dark breathers） of the H-MB equations. Finally, we also construct the rogue wave solutions of the above system.
文摘We present the spin polarized calculations on the new Zr2NiX (X = Al, Ga) alloys. Band structure analysis present them as half-metallic compounds with integral spin magnetic moment of 3 B following the general Slater-Pauling rule. Thermal effects on some macroscopic properties using quasi-harmonic Debye model which considers the phononic effects, the effects of pressure and temperature are taken into account. The variations of the thermal expansion coefficient, Debye temperature, Gruneisen parameter and heat capacity for the compounds have been investigated for the first time. These thermodynamic properties may prove as a reference for their synthesis.
基金supported by the grants from the Ministry of Science and Technology of Chinathe Ministry of Education+2 种基金support from the ARL and the AFOSR MURI programssupported by JQI-NSF-PFCLPS-MPO-CMTC
文摘Hopf insulators are intriguing three-dimensional topological insulators characterized by an integer topological invariant. They originate from the mathematical theory of Hopf fibration and epitomize the deep connection between knot theory and topological phases of matter, which distinguishes them from other classes of topological insulators. Here, we implement a model Hamiltonian for Hopf insulators in a solid-state quantum simulator and report the first experimental observation of their topological properties, including nontrivial topological links associated with the Hopf fibration and the integer-valued topological invariant obtained from a direct tomographic measurement. Our observation of topological links and Hopf fibration in a quantum simulator opens the door to probe rich topological properties of Hopf insulators in experiments. The quantum simulation and probing methods are also applicable to the study of other intricate three-dimensional topological model Hamiltonians.
文摘We have shown here the results of PFEC(photofield emission current)calculated for GaAs(gallium arsenide).We have used the initial state wavefunctions derived using the Kronig-Penney potential model for evaluating the PFEC.We have found that PFEC is not oscillatory as obtained by Modinos and Klient,[Solid State Commun.50,651(1984)],but it is an exponential function.
文摘In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials(MMs) at will. We give three examples of metamaterial designs that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numerical simulations. Particular emphasis is put on the significance of such tailored effective properties of optical MMs.
基金supported by the ARL,the IARPA Logi Q program,and the AFOSR MURI programsupported by Tsinghua University for their visits+1 种基金the support from NSF under Grant No.PHY1402971.supported by JQI-NSF-PFC and LPS-MPO-CMTC at the final stage of this paper
文摘Knots and links are fascinating and intricate topological objects.Their influence spans from DNA and molecular chemistry to vortices in superfluid helium,defects in liquid crystals and cosmic strings in the early universe.Here we find that knotted structures also exist in a peculiar class of three-dimensional topological insulators—the Hopf insulators.In particular,we demonstrate that the momentum-space spin textures of Hopf insulators are twisted in a nontrivial way,which implies the presence of various knot and link structures.We further illustrate that the knots and nontrivial spin textures can be probed via standard time-of-flight images in cold atoms as preimage contours of spin orientations in stereographic coordinates.The extracted Hopf invariants,knots,and links are validated to be robust to typical experimental imperfections.Our work establishes the existence of knotted structures in Hopf insulators,which may have potential applications in spintronics and quantum information processing.
基金This work was carried out in part in the Materials Research Laboratory Central Facilities at the University of Illinois Urbana-ChampaignThis research is also part of the Delta research computing project,which is supported by the National Science Foundation(award OCI 2005572),and the State of Illinois.Delta is a joint effort of the University of Illinois Urbana-Champaign and its National Center for Super-computing Applications.
文摘The rise of automation and machine learning(ML)in electron microscopy has the potential to revolutionize materials research through autonomous data collection and processing.A significant challenge lies in developing ML models that rapidly generalize to large data sets under varying experimental conditions.We address this by employing a cycle generative adversarial network(CycleGAN)with a reciprocal space discriminator,which augments simulated data with realistic spatial frequency information.This allows the CycleGAN to generate images nearly indistinguishable from real data and provide labels for ML applications.We showcase our approach by training a fully convolutional network(FCN)to identify single atom defects in a 4.5 million atom data set,collected using automated acquisition in an aberration-corrected scanning transmission electron microscope(STEM).Our method produces adaptable FCNs that can adjust to dynamically changing experimental variables with minimal intervention,marking a crucial step towards fully autonomous harnessing of microscopy big data.
基金The project has received further funding from the European Research Council(ERC),Grant agreement No.101041159an Israel Science Foundation Grant No.1208/19.M.J.and H.R.K.gratefully acknowledge the National Supercomputing Mission of the Department of Science and Technology,India,and the Science and Engineering Research Board of the Department of Science and Technology,India,for financial support under Grants No.DST/NSM/R&D_HPC_Applications/2021/23 and No.SB/DF/005/2017,respectively+2 种基金Computational resources were provided by the Oak Ridge Leadership Computing Facility through the Innovative and Novel Computational Impact on Theory and Experiment(INCITE)program,which is a DOE Office of Science User Facility supported under Contract No.DE-AC05-00OR22725Supercomputer Education and Research Center at Indian Institute of Sciencethe ChemFarm cluster at the Weizmann Institute of Science.
文摘Moirésuperlattices of transition metal dichalcogenide(TMD)heterostructures give rise to rich excitonic phenomena associated with the interlayer twist angle.Theoretical calculations of excitons in such systems are typically based on model moirépotentials that mitigate the computational cost.However,predictive understanding of the electron-hole coupling dominating the excitations is crucial to realize the twist-induced modifications of the optical selection rules.In this work,we use many-body perturbation theory to evaluate the relation between twist angle and exciton properties in TMD heterostructures.We present an approach for unfolding excitonic states from the moiréBrillouin zone onto the separate-layer ones.Applying this method to a large-angle twisted MoS^(2)/MoSe^(2) bilayer,we find that the optical spectrum is dominated by mixed electron–hole transitions with different momenta in the separate monolayers,leading to unexpected hybridization between interlayer and intralayer excitons.Our findings offer a design pathway for exciton layer-localization in TMD heterostructures.
基金supported by JSPS Kakenhi(No.15K05141)from Japan Society for the Promotion of Science
文摘In three-dimensional noncentrosymmetric materials two-fold screw rotation symmetry forces electron＇s energy bands to have Weyl points at which two bands touch. This is illustrated for space groups No. 19 （P212121 ） and No. 198 （P213）, which have three orthogonal screw rotation axes. In the case of space groups No. 61 （Pbca） and No. 205 （Pa-3） that have extra inversion symmetry, Weyl points are promoted to four-fold degenerate line nodes in glide-invariant planes. The three-fold rotation symmetry present in the space groups No. 198 and No. 205 allows Weyl and Dirac points, respectively, to appear along its rotation axes in the Brillouin zone and generates four-fold and six-fold degeneracy at the F point and R point, respectively.
基金This study was supported by the Thuringian Ministry of Education,Science and Culture(OptiMi 2020-Graduate Research School‘Green Photonics’,B514-10061)the German Research Foundation(Leibniz program)the Carl Zeiss Foundation.
文摘In recent years,femtosecond(fs)-lasers have evolved into a versatile tool for high precision micromachining of transparent materials because nonlinear absorption in the focus can result in refractive index modifications or material disruptions.However,when high pulse energies or low numerical apertures are required,nonlinear side effects such as self-focusing,filamentation or white light generation can decrease the modification quality.In this paper,we apply simultaneous spatial and temporal focusing(SSTF)to overcome these limitations.The main advantage of SSTF is that the ultrashort pulse is only formed at the focal plane,thereby confining the intensity distribution strongly to the focal volume and suppressing detrimental nonlinear side effects.Thus,we investigate the optical breakdown within a water cell by pump-probe shadowgraphy,comparing conventional focusing and SSTF under equivalent focusing conditions.The plasma formation is well confined for low pulse energies,2 mJ,but higher pulse energies lead to the filamentation and break-up of the disruptions for conventional focusing,thereby decreasing the modification quality.In contrast,plasma induced by SSTF stays well confined to the focal plane,even for high pulse energies up to 8 mJ,preventing extended filaments,side branches or break-up of the disruptions.Furthermore,while conventional focusing leads to broadband supercontinuum generation,only marginal spectral broadening is observed using SSTF.These experimental findings are in excellent agreement with numerical simulations of the nonlinear pulse propagation and interaction processes.Therefore,SSTF appears to be a powerful tool to control the processing of transparent materials,e.g.,for precise ophthalmic fs-surgery.
文摘A planar honeycomb monolayer of siligraphene （SIC7） could be a prospective medium for clean energy storage due to its light weight, and its remarkable mechanical and unique electronic properties. By employing van der Waals- induced first principles calculations based on density functional theory （DFT）, we have explored the structural, electronic, and hydrogen （H2） storage characteristics of SiC7 sheets decorated with various light metals. The binding energies of lithium （Li）, sodium （Na）, potassium （K）, magnesium （Mg）, calcium （Ca）, scandium （Sc）, and titanium （Ti） dopants on a SiC7 monolayer were studied at various doping concentrations, and found to be strong enough to counteract the metal clustering effect. We further verified the stabilities of the metallized SiC7 sheets at room temperature using ab initio molecular dynamics （MD） simulations. Bader charge analysis revealed that upon adsorption, due to the difference in electronegativity, all the metal adatorns donated a fraction of their electronic charges to the SiC7 sheet. Each partially charged metal center on the SiC7 sheets could bind a maximum of 4 to 5 H2 molecules. A high H2 gravimetric density was achieved for several dopants at a doping concentration of 12.50%. The H2 binding energies were found to fall within the ideal range of 0.2-0.6 eV. Based on these findings, we propose that metal-doped SiC7 sheets can operate as efficient H2 storage media under ambient conditions.
基金Department of Energy under Award#DESC0019275 for the design of data-driven discovery pipeline and the first-principles computational workJ.Y.and C.X.L.acknowledge the support of DOE grant(DESC0019064)for the analytical model and symmetry analysis,and the Office of Naval Research(Grant number N00014-18-1-2793)+2 种基金as well as Kaufman New Initiative research grant of the Pittsburgh Foundation.A.J.acknowledges support from U.S.DOE SE-SC0014388S.X.D.thanks the International Partnership Program of Chinese Academy of Sciences,Grant number 112111KYSB20160061It benefitted from the supercomputing resources of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility operated under Contract number DE-AC02-05CH11231.
文摘Recent years have witnessed tremendous success in the discovery of topological states of matter.Particularly,sophisticated theoretical methods in time-reversal-invariant topological phases have been developed,leading to the comprehensive search of crystal database and the prediction of thousands of topological materials.In contrast,the discovery of magnetic topological phases that break time reversal is still limited to several exemplary materials because the coexistence of magnetism and topological electronic band structure is rare in a single compound.To overcome this challenge,we propose an alternative approach to realize the quantum anomalous Hall(QAH)effect,a typical example of magnetic topological phase,via engineering two-dimensional(2D)magnetic van der Waals heterojunctions.
基金supported by the National Natural Science Foundation of China (11347007)Qing Lan Project, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), Jiangsu Overseas Research and Training Program for University Prominent Young and Middle-aged Teachers and Presidents
文摘The structural, dynamical, and electronic properties of compressed Sr C2 were systematically investigated up to 200 GPa by using ab initio method. Three new phases are obtained by means of evolutionary algorithm. The confirmed most stable structure has C2/c symmetry at zero pressure, which transforms into an orthorhombic Cmcm phase at 4.5 GPa, followed by another orthorhombic Immm phase, which is stabilized at wide pressure range of 21.5–123.5 GPa, and then transformed into Mg B2-type phase(space group, P6/mmm). Although Sr C2 has similar structural transformation to that of compressed Ca C2, Sr C2 holds small electron–phonon coupling,which leads to its low superconducting critical temperature(only 1.8 K).
