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
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
The nonlinear Wannier functions in square Kronig-Penney potential are investigated with the help of a set of exact nonlinear Bloch solutions. The nonlinear interaction makes the Wannier functions fall off as non-expon...The nonlinear Wannier functions in square Kronig-Penney potential are investigated with the help of a set of exact nonlinear Bloch solutions. The nonlinear interaction makes the Wannier functions fall off as non-exponential law with distance and enhances the tunneling coupling between the neighbor sites.展开更多
I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functionai theory （...I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functionai theory （DFT）. The DFT eigenvectors are then transformed into a set of maximaily localized Wannier functions （MLWFs） [N. Maxzari and D. Vanderbilt, Phys. Rev. B 56 （1997） 12847]. The MLWFs are used as a minimai basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green＇s function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green＇s function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires （Cu and Pt）. It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomie wire due to the contribution of d-orbitals at the Fermi energy,展开更多
We investigate the interactions of lattice pbonons with Wannier-Mott exciton, the exciton that has a large radius in two-dimensional molecular lattice, by the method of continuum limit approximation, and obtain that t...We investigate the interactions of lattice pbonons with Wannier-Mott exciton, the exciton that has a large radius in two-dimensional molecular lattice, by the method of continuum limit approximation, and obtain that the self-trapping can also appear in two-dimensional molecular lattice with a harmonic and nonlinear potential. The exciton effect on molecular lattice does not distort the molecular lattice but only makes it localized and the localization can also react, again through phonon coupling, to trap the energy and prevents its dispersion.展开更多
We present here a formulation of subdynamics to calculatee Wannier-Mott excitons in a Nami-semiconductor driven by a strong electrical field. The formula of the evolution of density operator for the time-dependent Lio...We present here a formulation of subdynamics to calculatee Wannier-Mott excitons in a Nami-semiconductor driven by a strong electrical field. The formula of the evolution of density operator for the time-dependent Liouvillian is given. In terms of this formula rue can calculate the nonlinear response of the absorbing coefficient of light for nami-semicouducton. The results are helpful to study either the nonlinear behavior of the Wannier-Mott excitons in a nami-semicouducton driven by a strong harmonic field or the optic properties of these Kinds of materials.展开更多
In this paper, the electronic transfer integrals, the energy gap, and the bandwidth of a planar trans polyacetylene chain are calculated in Wannier representation, in which a combination of the wave function of hydrog...In this paper, the electronic transfer integrals, the energy gap, and the bandwidth of a planar trans polyacetylene chain are calculated in Wannier representation, in which a combination of the wave function of hydrogen like atoms is used to stand for the Wannier function. When the effective nuclear charge number Z = 2.125 and the distortion amplitude of the carbon sites u =0.0038 nm, the nearest, next, and third neighbor hopping energies obtained are -3.224 78 eV, -2.388 61 eV, 0.148 14 eV, 0.006 65 eV, and 0.006 50 eV, respectively. The energy bandwidth and gap corresponding to these values are W d =11.19 eV and E g =1.70 eV, respectively. These results coincide with the experimental values.展开更多
We present a scattering theory for charged particles suitable for electron atom collisions. Starting from the Hamilton-Jacobi equation for N electrons in the field of a nucleus or an ion core, we derive a parabolic di...We present a scattering theory for charged particles suitable for electron atom collisions. Starting from the Hamilton-Jacobi equation for N electrons in the field of a nucleus or an ion core, we derive a parabolic differential equation that resembles the heat equation. We identify a Fresnel distribution as the main ingredient of its kernel. In particular, we show that high multiply excited states are strongly suppressed increasingly so for approaching the ionization threshold. That effect compares favorably with experimental data. Also, the Wannier channel is controlled by a Fresnel distribution. Moreover, that channel represents a novel continuum to our knowledge that has never been considered so far. The classical action has been employed to derive quatum wave functions in the semiclassical limit. The curvature of the N-elctron potential surface is shown to be the essential ingredient of an initial value problem for elastic and/or inelastic processes. The spectral region near the ionization threshold needs a special action to describe the Wannier phenomenon. This Wannier channel manifests itself by a novel continuum never considered before.展开更多
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Project supported by the National Natural Science Foundation of China (Grant No 10674087)973 Program (Grant Nos 2006CB921603 and 2008CB317103)+2 种基金the Natural Science Foundation of Shanxi Province of China (Grant No 200611004)NCET(NCET-06-0259)IMR SYNL-T.S. Kê Research Fellowship
文摘The nonlinear Wannier functions in square Kronig-Penney potential are investigated with the help of a set of exact nonlinear Bloch solutions. The nonlinear interaction makes the Wannier functions fall off as non-exponential law with distance and enhances the tunneling coupling between the neighbor sites.
基金Support from Ningbo Science Foundation under Grant No.2010A610179also from the Start-Up Fund and K.C.Wong Magna Fund in Ningbo University
文摘I present a method to calculate the ballistic transport properties of atomic-scale structures under bias. The electronic structure of the system is calculated using the Kohn-Sham scheme of density functionai theory （DFT）. The DFT eigenvectors are then transformed into a set of maximaily localized Wannier functions （MLWFs） [N. Maxzari and D. Vanderbilt, Phys. Rev. B 56 （1997） 12847]. The MLWFs are used as a minimai basis set to obtain the Hamitonian matrices of the scattering region and the adjacent leads, which are needed for transport calculation using the nonequilibrium Green＇s function formalism. The coupling of the scattering region to the semi-infinite leads is described by the self-energies of the leads. Using the nonequilibrium Green＇s function method, one calculates self-consistently the charge distribution of the system under bias and evaluates the transmission and current through the system. To solve the Poisson equation within the scheme of MLWFs I introduce a computationally efficient method. The method is applied to a molecular hydrogen contact in two transition metal monatomic wires （Cu and Pt）. It is found that for Pt the I-V characteristics is approximately linear dependence, however, for Cu the I-V characteristics manifests a linear dependence at low bias voltages and exhibits apparent nonlinearity at higher bias voltages. I have also calculated the transmission in the zero bias voltage limit for a single CO molecule adsorbed on Cu and Pt monatomic wires. While a chemical scissor effect occurs for the Cu monatomic wire with an adsorbed CO molecule, it is absent for the Pt monatomie wire due to the contribution of d-orbitals at the Fermi energy,
基金supported by the National Natural Science Foundation of China (Grant No.1057400)the Natural Science Foundation of Heilongjiang Province,China (Grant No.A200506)
文摘We investigate the interactions of lattice pbonons with Wannier-Mott exciton, the exciton that has a large radius in two-dimensional molecular lattice, by the method of continuum limit approximation, and obtain that the self-trapping can also appear in two-dimensional molecular lattice with a harmonic and nonlinear potential. The exciton effect on molecular lattice does not distort the molecular lattice but only makes it localized and the localization can also react, again through phonon coupling, to trap the energy and prevents its dispersion.
文摘We present here a formulation of subdynamics to calculatee Wannier-Mott excitons in a Nami-semiconductor driven by a strong electrical field. The formula of the evolution of density operator for the time-dependent Liouvillian is given. In terms of this formula rue can calculate the nonlinear response of the absorbing coefficient of light for nami-semicouducton. The results are helpful to study either the nonlinear behavior of the Wannier-Mott excitons in a nami-semicouducton driven by a strong harmonic field or the optic properties of these Kinds of materials.
文摘In this paper, the electronic transfer integrals, the energy gap, and the bandwidth of a planar trans polyacetylene chain are calculated in Wannier representation, in which a combination of the wave function of hydrogen like atoms is used to stand for the Wannier function. When the effective nuclear charge number Z = 2.125 and the distortion amplitude of the carbon sites u =0.0038 nm, the nearest, next, and third neighbor hopping energies obtained are -3.224 78 eV, -2.388 61 eV, 0.148 14 eV, 0.006 65 eV, and 0.006 50 eV, respectively. The energy bandwidth and gap corresponding to these values are W d =11.19 eV and E g =1.70 eV, respectively. These results coincide with the experimental values.
文摘We present a scattering theory for charged particles suitable for electron atom collisions. Starting from the Hamilton-Jacobi equation for N electrons in the field of a nucleus or an ion core, we derive a parabolic differential equation that resembles the heat equation. We identify a Fresnel distribution as the main ingredient of its kernel. In particular, we show that high multiply excited states are strongly suppressed increasingly so for approaching the ionization threshold. That effect compares favorably with experimental data. Also, the Wannier channel is controlled by a Fresnel distribution. Moreover, that channel represents a novel continuum to our knowledge that has never been considered so far. The classical action has been employed to derive quatum wave functions in the semiclassical limit. The curvature of the N-elctron potential surface is shown to be the essential ingredient of an initial value problem for elastic and/or inelastic processes. The spectral region near the ionization threshold needs a special action to describe the Wannier phenomenon. This Wannier channel manifests itself by a novel continuum never considered before.
