We theoretically explore higher-order topological magnons in collinear altermagnets,encompassing a dimensional hierarchy ranging from localized corner modes to propagating hinge excitations.By employing antiferromagne...We theoretically explore higher-order topological magnons in collinear altermagnets,encompassing a dimensional hierarchy ranging from localized corner modes to propagating hinge excitations.By employing antiferromagnetic interlayer coupling in bosonic Bogoliubov–de Gennes Hamiltonian,our work reveals anisotropic surface states and spatially distributed hinge modes propagating along facet intersections.We track the adiabatic evolution of Wannier centers to identify the bulk polarization with second-order topological magnon insulator,where various magnon spectra demonstrate symmetry-protected band structure beyond conventional topology.Leveraging the stability and propagative properties of hinge modes,these unconventional magnons demonstrate manipulability in atomic-scale modifications of termination.Our study integrates altermagnetism with higher-order topology,which advances magnon-based quantum computing processing energy-efficient integrated architectures and information transfer.展开更多
Maximally-localized Wannier functions(MLWFs)are widely employed as an essential tool for calculating the physical properties of materials due to their localized nature and computational efficiency.Projectability-disen...Maximally-localized Wannier functions(MLWFs)are widely employed as an essential tool for calculating the physical properties of materials due to their localized nature and computational efficiency.Projectability-disentangled Wannier functions(PDWFs)have recently emerged as a reliable and efficient approach for automatically constructing MLWFs that span both occupied and lowest unoccupied bands.Here,we extend the applicability of PDWFs to magnetic systems and/or those including spin-orbit coupling,and implement such extensions in automated workflows.Furthermore,we enhance the robustness and reliability of constructing PDWFs by defining an extended protocol that automatically expands the projectors manifold,when required,by introducing additional appropriate hydrogenic atomic orbitals.We benchmark our extended protocol on a set of 200 chemically diverse materials,as well as on the 40 systems with the largest band distance obtained with the standard PDWF approach,showing that on our test set the present approach delivers a success rate of over 98%in obtaining accurate Wannier-function interpolations,defined as an average band distance below20 meV between the DFT and Wannier-interpolated bands,up to 2 eV above the Fermi level for metals or above the conduction band minimum for insulators(and a 100%success rate when including only bands up to 1 eV above these values).展开更多
Topological materials are often characterized by unique edge states which are in turn used to detect different topological phases in experiments.Recently,with the discovery of various higher-order topological insulato...Topological materials are often characterized by unique edge states which are in turn used to detect different topological phases in experiments.Recently,with the discovery of various higher-order topological insulators,such spectral topological characteristics are extended from edge states to corner states.However,the chiral symmetry protecting the corner states is often broken in genuine materials,leading to vulnerable corner states even when the higher-order topological numbers remain quantized and invariant.Here,we show that a local artificial gauge flux can serve as a robust probe of the Wannier type higher-order topological insulators,which is effective even when the chiral symmetry is broken.The resultant observable signature is the emergence of the cyclic spectral flows traversing one or multiple band gaps.These spectral flows are associated with the local modes bound to the artificial gauge flux.This phenomenon is essentially due to the cyclic transformation of the Wannier orbitals when the local gauge flux acts on them.We extend topological Wannier cycles to systems with C_(2)and C_(3)symmetries and show that they can probe both the bulk and the edge Wannier centers,yielding rich topological phenomena.展开更多
Two-electron atoms have been investigated near threshold of double escape within the framework of hyperspherical coordinates. A particularly useful set of hyperspherical angles has been used. It is well known for many...Two-electron atoms have been investigated near threshold of double escape within the framework of hyperspherical coordinates. A particularly useful set of hyperspherical angles has been used. It is well known for many years that the hyperradial motion is nearly separable from the hyperspherical angular motion. Therefore, the Born-Oppenheimer separation method should be useful. However, the success of that method in molecular physics is based on the small mass ratio, electron mass to nuclear mass. In the atomic application such a small parameter does not exist. Nevertheless the method works surprisingly well in the lower part of the spectrum. For increasing excitation energy the method becomes shaky. Near ionization threshold, it breaks even down. The author will present elsewhere an improved Born-Oppenheimer method. First pilot developments and comparison with the experimental situation are presented already here. Inclusion of a momentum-momentum radial coupling delivers an improved basis. We show that our extended Born-Oppenheimer approach leads to a deformation of the whole potential energy surface during the collision. In consequence of this deformation we outline a quantum derivation of the Wannier threshold cross section law, and we show that (e, 2e) angular distribution data are strongly influenced by that surface deformation. Finally, we present a mechanism for electron pair formation and decay leading to a supercurrent independent of the temperature. Our framework can be extended to more than two electrons, say 3 or 4. We conclude that our improved Born-Oppenheimer method <a href="#ref.1">[1]</a> is expected not only to deliver better numerical data, but it is expected to describe also the Wannier phenomenon. The idea of the new theory together with first qualitative results is presented in this paper.展开更多
We present an improved Born-Oppenheimer method for the treatment of molecules. Our development is based on taking into account a portion of the kinetic energy which was inadvertently omitted by Born and Oppenheimer. O...We present an improved Born-Oppenheimer method for the treatment of molecules. Our development is based on taking into account a portion of the kinetic energy which was inadvertently omitted by Born and Oppenheimer. Our theory replaces the set of standard atom-atom potentials by an evolution operator. In particular, in contrast to the traditional Born-Oppenheimer method our amended basis describes the so-called Wannier phenomenon which deforms potential surfaces, and traps one or more threshold electrons into an unstable equilibrium. Within our framework that trapping manifests itself as a Fresnel distribution. Finally we discover a π/2 phase jump in the evolution operator caused by the diffraction of a two-electron wave from a potential ridge.展开更多
We employ a recently amended Born-Oppenheimer (hereafter shortly BO) approximation <a href="#1">[1]</a> to treat inelastic scattering of slow electrons from highly excited Rydberg atoms like e<...We employ a recently amended Born-Oppenheimer (hereafter shortly BO) approximation <a href="#1">[1]</a> to treat inelastic scattering of slow electrons from highly excited Rydberg atoms like e<sup>-</sup> + He(1<em>s</em> <em>n</em><em>s</em>)→He<sup>-** </sup>for <em>n</em> <span style="white-space:nowrap;">≫</span> 1. Along these lines we replace the standard BO set of potentials by an evolution operator. In this way we take a momentum-momentum coupling inadvertently disregarded by BO into account. The BO eigenvalue problem is now replaced by an evolution equation. One eigen-evolution has been identified as Wanner channel. That channel describes the diffraction of electron pairs from a potential ridge. That diffraction causes a phase jump of π/2 in the channel evolution. Moreover we present a new conservative attractive force controlling the motion of the electron pair as a whole in the nuclear field whose potential is given by <img src="Edit_b22c3b40-4eb3-4060-aa36-c333530638c6.bmp" alt="" />. The coupling constant <em>g</em> has been calculated. That potential foreign to the standard BO approximation manifests itself by an entirely new series of isolated resonances located slightly below the double ionization threshold. This resonance ensemble compares favorably with experimental data. Further we present an evolution which forces the electron pair to the electrostatically unstable top of the potential ridge. That evolution may be regarded as quantum version of Wannier’s converging trajectory, and manifests itself here as Fresnel distribution.展开更多
Topological defects(including disclinations and dislocations)which commonly exist in various materials have shown an amazing ability to produce excellent mechanical and physical properties of matters.In this paper,dis...Topological defects(including disclinations and dislocations)which commonly exist in various materials have shown an amazing ability to produce excellent mechanical and physical properties of matters.In this paper,disclinations are introduced into topological nontrivial elastic phononic plates.The deformation of the lattice yielded by disclinations produces a pentagonal core with the local five-fold symmetry.The topological bound states are well localized around the boundaries of the pentagonal cores with and without hollow regions.The topological bound states immunize against the finite sizes and the moderate imperfects of plates,essentially differing from the trivial defect states.The discovery of topological bound states unveils a new horizon in topological mechanics and physics,and it provides a novel platfonn to implement large-scale elastic devices with topologically protected resonances.展开更多
Based on the first-principles density functional theory electronic structure calculation,we investigate the possible phonon-mediated superconductivity in arsenene,a two-dimensional buckled arsenic atomic sheet,under e...Based on the first-principles density functional theory electronic structure calculation,we investigate the possible phonon-mediated superconductivity in arsenene,a two-dimensional buckled arsenic atomic sheet,under electron doping.We find that the strong superconducting pairing interaction results mainly from the pz-like electrons of arsenic atoms and the A1 phonon mode around the K point,and the superconducting transition temperature can be as high as 30.8 K in the arsenene with 0.2 doped electrons per unit cell and 12%-applied biaxial tensile strain.This transition temperature is about ten times higher than that in the bulk arsenic under high pressure.It is also the highest transition temperature that is predicted for electron-doped two-dimensional elemental superconductors,including graphene,silicene,phosphorene,and borophene.展开更多
Based on density functional first-principles calculations and anisotropic Eliashberg equations,we have investigated the electronic structure,lattice dynamics,and phonon-mediated superconductivity in newly synthesized ...Based on density functional first-principles calculations and anisotropic Eliashberg equations,we have investigated the electronic structure,lattice dynamics,and phonon-mediated superconductivity in newly synthesized layered compound Sr BC under pressure.Different from Li BC and Mg B2,our calculations surprisingly reveal that Sr BC is isotropic in compressibility,due to the accumulation of substantial electrons in the interstitial region.We find that the Sr phonons strongly couple with B-2 pz orbital and the interstitial states,giving rise to a two-gap superconductivity in Sr BC,whose transition temperature shows an inverted V-shaped dependence on pressure.The maximal transition temperature is about 22 K at50 GPa.On both sides of 50 GPa,the transition temperature exhibits quasi-linear variation with positive and negative slopes,respectively.Such a variation of transition temperature is infrequent among phonon-mediated superconductors.The competition between enhanced electron–phonon matrix element and hardened phonons plays an essential role in governing the behavior of the critical temperature.展开更多
We study the double ionization dynamics of a helium atom impacted by electrons with full-dimensional classical trajectory Monte Carlo simulation. The excess energy is chosen to cover a wide range of values from 5 e V ...We study the double ionization dynamics of a helium atom impacted by electrons with full-dimensional classical trajectory Monte Carlo simulation. The excess energy is chosen to cover a wide range of values from 5 e V to 1 ke V for comparative study. At the lowest excess energy, i.e., close to the double-ionization threshold, it is found that the projectile momentum is totally transferred to the recoil-ion while the residual energy is randomly partitioned among the three outgoing electrons, which are then most probably emitted with an equilateral triangle configuration. Our results agree well with experiments as compared with early quantum-mechanical calculation as well as classical simulation based on a two-dimensional Bohr's model. Furthermore, by mapping the final momentum vectors event by event into a Dalitz plot,we unambiguously demonstrate that the ergodicity has been reached and thus confirm a long-term scenario conceived by Wannier. The time scale for such few-body thermalization, from the initial nonequilibrium state to the final microcanonical distribution, is only about 100 attoseconds. Finally, we predict that, with the increase of the excess energy, the dominant emission configuration undergoes a transition from equilateral triangle to T-shape and finally to a co-linear mode. The associated signatures of such configuration transition in the electron–ion joint momentum spectrum and triple-electron angular distribution are also demonstrated.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1402802)the National Natural Science Foundation of China(Grant Nos.92165204 and 12494591)+2 种基金Guangdong Provincial Key Laboratory of Magnetoelectric Physics and Devices(Grant No.2022B1212010008)Research Center for Magnetoelectric Physics of Guangdong Province(Grant No.2024B0303390001)Guangdong Provincial Quantum Science Strategic Initiative(Grant No.GDZX2401010)。
文摘We theoretically explore higher-order topological magnons in collinear altermagnets,encompassing a dimensional hierarchy ranging from localized corner modes to propagating hinge excitations.By employing antiferromagnetic interlayer coupling in bosonic Bogoliubov–de Gennes Hamiltonian,our work reveals anisotropic surface states and spatially distributed hinge modes propagating along facet intersections.We track the adiabatic evolution of Wannier centers to identify the bulk polarization with second-order topological magnon insulator,where various magnon spectra demonstrate symmetry-protected band structure beyond conventional topology.Leveraging the stability and propagative properties of hinge modes,these unconventional magnons demonstrate manipulability in atomic-scale modifications of termination.Our study integrates altermagnetism with higher-order topology,which advances magnon-based quantum computing processing energy-efficient integrated architectures and information transfer.
基金supported by the NCCR MARVEL,a National Center of Competence in Research,funded by the Swiss National Science Foundation(grant number 205602)YJ acknowledge support by the China Scholarship Council program+5 种基金JQ acknowledges support by the HORIZON-RIA 2D-PRINTABLE(proposal number:101135196)this work has received funding from the Swiss State Secretariat for Education,Research and Innovation(SERI)NP and GP acknowledge support by the Swiss National Science Foundation(SNSF)Project Funding(grant 200021E_206190 FISH4DIET)WZ acknowledge support by the National Key Research and Development Program of China(Grant No.2022YFB4400200)National Natural Science Foundation of China(Grant Nos.T2394474,T2394470)the Beijing Outstanding Young Scientist Program and Tencent Foundation through the XPLORER PRIZE.We acknowledge access to Piz Daint or Alps at the Swiss National Supercomputing Center,Switzerland under MARVEL's share with the project ID mr32.We acknowledge fruitful discussions with Edward Baxter Linscott and Miki Bonacci.
文摘Maximally-localized Wannier functions(MLWFs)are widely employed as an essential tool for calculating the physical properties of materials due to their localized nature and computational efficiency.Projectability-disentangled Wannier functions(PDWFs)have recently emerged as a reliable and efficient approach for automatically constructing MLWFs that span both occupied and lowest unoccupied bands.Here,we extend the applicability of PDWFs to magnetic systems and/or those including spin-orbit coupling,and implement such extensions in automated workflows.Furthermore,we enhance the robustness and reliability of constructing PDWFs by defining an extended protocol that automatically expands the projectors manifold,when required,by introducing additional appropriate hydrogenic atomic orbitals.We benchmark our extended protocol on a set of 200 chemically diverse materials,as well as on the 40 systems with the largest band distance obtained with the standard PDWF approach,showing that on our test set the present approach delivers a success rate of over 98%in obtaining accurate Wannier-function interpolations,defined as an average band distance below20 meV between the DFT and Wannier-interpolated bands,up to 2 eV above the Fermi level for metals or above the conduction band minimum for insulators(and a 100%success rate when including only bands up to 1 eV above these values).
基金supported by the National Natural Science Foundation of China(Grant Nos.12125504 and 12074281)。
文摘Topological materials are often characterized by unique edge states which are in turn used to detect different topological phases in experiments.Recently,with the discovery of various higher-order topological insulators,such spectral topological characteristics are extended from edge states to corner states.However,the chiral symmetry protecting the corner states is often broken in genuine materials,leading to vulnerable corner states even when the higher-order topological numbers remain quantized and invariant.Here,we show that a local artificial gauge flux can serve as a robust probe of the Wannier type higher-order topological insulators,which is effective even when the chiral symmetry is broken.The resultant observable signature is the emergence of the cyclic spectral flows traversing one or multiple band gaps.These spectral flows are associated with the local modes bound to the artificial gauge flux.This phenomenon is essentially due to the cyclic transformation of the Wannier orbitals when the local gauge flux acts on them.We extend topological Wannier cycles to systems with C_(2)and C_(3)symmetries and show that they can probe both the bulk and the edge Wannier centers,yielding rich topological phenomena.
文摘Two-electron atoms have been investigated near threshold of double escape within the framework of hyperspherical coordinates. A particularly useful set of hyperspherical angles has been used. It is well known for many years that the hyperradial motion is nearly separable from the hyperspherical angular motion. Therefore, the Born-Oppenheimer separation method should be useful. However, the success of that method in molecular physics is based on the small mass ratio, electron mass to nuclear mass. In the atomic application such a small parameter does not exist. Nevertheless the method works surprisingly well in the lower part of the spectrum. For increasing excitation energy the method becomes shaky. Near ionization threshold, it breaks even down. The author will present elsewhere an improved Born-Oppenheimer method. First pilot developments and comparison with the experimental situation are presented already here. Inclusion of a momentum-momentum radial coupling delivers an improved basis. We show that our extended Born-Oppenheimer approach leads to a deformation of the whole potential energy surface during the collision. In consequence of this deformation we outline a quantum derivation of the Wannier threshold cross section law, and we show that (e, 2e) angular distribution data are strongly influenced by that surface deformation. Finally, we present a mechanism for electron pair formation and decay leading to a supercurrent independent of the temperature. Our framework can be extended to more than two electrons, say 3 or 4. We conclude that our improved Born-Oppenheimer method <a href="#ref.1">[1]</a> is expected not only to deliver better numerical data, but it is expected to describe also the Wannier phenomenon. The idea of the new theory together with first qualitative results is presented in this paper.
文摘We present an improved Born-Oppenheimer method for the treatment of molecules. Our development is based on taking into account a portion of the kinetic energy which was inadvertently omitted by Born and Oppenheimer. Our theory replaces the set of standard atom-atom potentials by an evolution operator. In particular, in contrast to the traditional Born-Oppenheimer method our amended basis describes the so-called Wannier phenomenon which deforms potential surfaces, and traps one or more threshold electrons into an unstable equilibrium. Within our framework that trapping manifests itself as a Fresnel distribution. Finally we discover a π/2 phase jump in the evolution operator caused by the diffraction of a two-electron wave from a potential ridge.
文摘We employ a recently amended Born-Oppenheimer (hereafter shortly BO) approximation <a href="#1">[1]</a> to treat inelastic scattering of slow electrons from highly excited Rydberg atoms like e<sup>-</sup> + He(1<em>s</em> <em>n</em><em>s</em>)→He<sup>-** </sup>for <em>n</em> <span style="white-space:nowrap;">≫</span> 1. Along these lines we replace the standard BO set of potentials by an evolution operator. In this way we take a momentum-momentum coupling inadvertently disregarded by BO into account. The BO eigenvalue problem is now replaced by an evolution equation. One eigen-evolution has been identified as Wanner channel. That channel describes the diffraction of electron pairs from a potential ridge. That diffraction causes a phase jump of π/2 in the channel evolution. Moreover we present a new conservative attractive force controlling the motion of the electron pair as a whole in the nuclear field whose potential is given by <img src="Edit_b22c3b40-4eb3-4060-aa36-c333530638c6.bmp" alt="" />. The coupling constant <em>g</em> has been calculated. That potential foreign to the standard BO approximation manifests itself by an entirely new series of isolated resonances located slightly below the double ionization threshold. This resonance ensemble compares favorably with experimental data. Further we present an evolution which forces the electron pair to the electrostatically unstable top of the potential ridge. That evolution may be regarded as quantum version of Wannier’s converging trajectory, and manifests itself here as Fresnel distribution.
基金supported by the National Natural Science Foundation of China(Grant Nos.12072108 and 51621004)Hunan Provincial Natural Science Foundation of China(Grant No.2021JJ40626).
文摘Topological defects(including disclinations and dislocations)which commonly exist in various materials have shown an amazing ability to produce excellent mechanical and physical properties of matters.In this paper,disclinations are introduced into topological nontrivial elastic phononic plates.The deformation of the lattice yielded by disclinations produces a pentagonal core with the local five-fold symmetry.The topological bound states are well localized around the boundaries of the pentagonal cores with and without hollow regions.The topological bound states immunize against the finite sizes and the moderate imperfects of plates,essentially differing from the trivial defect states.The discovery of topological bound states unveils a new horizon in topological mechanics and physics,and it provides a novel platfonn to implement large-scale elastic devices with topologically protected resonances.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0302901)the National Natural Science Foundation of China(Grant Nos.11474331,11404383,and 11474004)+1 种基金the Natural Science Foundation of Zhejiang Province,China(Grant No.LY17A040005)the K.C.Wong Magna Fund in Ningbo University
文摘Based on the first-principles density functional theory electronic structure calculation,we investigate the possible phonon-mediated superconductivity in arsenene,a two-dimensional buckled arsenic atomic sheet,under electron doping.We find that the strong superconducting pairing interaction results mainly from the pz-like electrons of arsenic atoms and the A1 phonon mode around the K point,and the superconducting transition temperature can be as high as 30.8 K in the arsenene with 0.2 doped electrons per unit cell and 12%-applied biaxial tensile strain.This transition temperature is about ten times higher than that in the bulk arsenic under high pressure.It is also the highest transition temperature that is predicted for electron-doped two-dimensional elemental superconductors,including graphene,silicene,phosphorene,and borophene.
基金the National Natural Science Foundation of China(Grant Nos.11974194 and 11974207)K.C.Wong Magna Fund in Ningbo University。
文摘Based on density functional first-principles calculations and anisotropic Eliashberg equations,we have investigated the electronic structure,lattice dynamics,and phonon-mediated superconductivity in newly synthesized layered compound Sr BC under pressure.Different from Li BC and Mg B2,our calculations surprisingly reveal that Sr BC is isotropic in compressibility,due to the accumulation of substantial electrons in the interstitial region.We find that the Sr phonons strongly couple with B-2 pz orbital and the interstitial states,giving rise to a two-gap superconductivity in Sr BC,whose transition temperature shows an inverted V-shaped dependence on pressure.The maximal transition temperature is about 22 K at50 GPa.On both sides of 50 GPa,the transition temperature exhibits quasi-linear variation with positive and negative slopes,respectively.Such a variation of transition temperature is infrequent among phonon-mediated superconductors.The competition between enhanced electron–phonon matrix element and hardened phonons plays an essential role in governing the behavior of the critical temperature.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12174034, 12047510, and 11822401)NSAF (Grant Nos. U1930402 and U1930403)。
文摘We study the double ionization dynamics of a helium atom impacted by electrons with full-dimensional classical trajectory Monte Carlo simulation. The excess energy is chosen to cover a wide range of values from 5 e V to 1 ke V for comparative study. At the lowest excess energy, i.e., close to the double-ionization threshold, it is found that the projectile momentum is totally transferred to the recoil-ion while the residual energy is randomly partitioned among the three outgoing electrons, which are then most probably emitted with an equilateral triangle configuration. Our results agree well with experiments as compared with early quantum-mechanical calculation as well as classical simulation based on a two-dimensional Bohr's model. Furthermore, by mapping the final momentum vectors event by event into a Dalitz plot,we unambiguously demonstrate that the ergodicity has been reached and thus confirm a long-term scenario conceived by Wannier. The time scale for such few-body thermalization, from the initial nonequilibrium state to the final microcanonical distribution, is only about 100 attoseconds. Finally, we predict that, with the increase of the excess energy, the dominant emission configuration undergoes a transition from equilateral triangle to T-shape and finally to a co-linear mode. The associated signatures of such configuration transition in the electron–ion joint momentum spectrum and triple-electron angular distribution are also demonstrated.
