Interatomic Coulomb Interactions Research Articles

Magnetc states in the surface dimer model for adsorption

For the electrons of surface dimer formed by adsorbed particle and substrate atom effects of the intra- and interatomic Coulomb interactions are taken into account. Two cases are considered: adsorption of magnetic particle on nonmagnetic substrate and adsorption of nonmagnetic particle on magnetic substrate. Analytical expressions for the surface dimer magnetization are obtained for the regimes of weak and strong dimer --- substrate coupling. Keywords: adsorbate, substrate, occupation number, magnetization

Магнитные состояния в модели поверхностного димера

For the electrons of surface dimer formed by adsorbed particle and substrate atom effects of the intra- and interatomic Coulomb interactions are taken into account. Two cases are considered: adsorption of magnetic particle on nonmagnetic substrate and adsorption of nonmagnetic particle on magnetic substrate. Analytical expressions for the surface dimer magnetization are obtained for the regimes of weak and strong dimer – substrate coupling

Occurrence of Topologically Nontrivial Phases, Cascade of Quantum Transitions, and Identification of Majorana Modes in Chiral Superconductors and Nanowires (Scientific Summary)

The problems of occurrence and experimental identification of topologically nontrivial phases in condensed matter have been reviewed. The results of the study of the effect of strong intra- and interatomic Coulomb interaction on a quantum phase transition with change in the topological index in an ensemble of Hubbard fermions on a triangular lattice have been reported. Nontrivial topology of the phase of coexistence of d + id chiral superconductivity and 120° spin ordering in a system with the triangular lattice has been discussed and the formation of Majorana modes in such a phase has been demonstrated. A cascade of quantum transitions that occurs at the variation of the magnetic field or the electrochemical potential has been analyzed for an open nanowire with the Rashba spin-orbit coupling and the induced superconducting pairing potential. It has been shown that anomalies of magneto- and electrocaloric effects are manifested near such quantum transitions and can be used to experimentally test materials on the existence of topologically nontrivial phases in them. The switching of the spin-polarized current in the topological superconducting phase has been predicted for a semimetal/superconducting wire/semimetal structure in the weak nonequilibrium regime.

Coexistence of Superconductivity and Antiferromagnetism in High-T C Gd1+x Ba2−x Cu3O7−δ Superconductor

Following the experimental discovery of the coexistence of superconductivity and antiferromagnetism in high- TC superconductor of fully oxygenated superconducting Gd1.2Ba1.8Cu3O7.03 by Rogacki, a theoretical study has been made by considering a model Hamiltonian consisting of pairing interaction, intra- and inter-atomic Coulomb interactions, exchange interaction, and a new interaction involving scattering of Cooper pairs by the magnetic moments/spins of Gd ions. Employing Green’s function formalism and a suitable decoupling approximation technique, the coexistence of superconductivity and antiferromagnetism has been shown to be a very distinct possibility. The phase diagrams of superconducting gap parameter (Δ) versus temperature (T) for various values of magnetic order parameter (η), the superconducting transition temperature (TC) and antiferromagnetism order temperature (TN) versus magnetic order parameter (η) have been plotted. Finally, by combining the two phase diagrams, the coexistence of superconductivity and antiferromagnetism has been demonstrated. The obtained result is in broad agreement with the experimental observations.

Phase diagram of the Kohn-Luttinger superconducting state for bilayer graphene

The effect of the intersite and interplane Coulomb interactions between the Dirac fermions on the formation of the Kohn-Luttinger superconductivity in bilayer doped graphene is studied disregarding the effects of the van der Waals potential of the substrate and both magnetic and non-magnetic impurities. The phase diagram determining the boundaries of superconductive domains with different types of symmetry of the order parameter is built using the extended Hubbard model in the Born weak-coupling approximation with allowance for the intratomic, interatomic, and interlayer Coulomb interactions between electrons. It is shown that the Kohn-Luttinger polarization contributions up to the second order of perturbation theory in the Coulomb interaction inclusively and an account for the long-range intraplane Coulomb interactions significantly affect the competition between the superconducting $f-$, $p+ip-$, and $d+id-$wave pairings. It is demonstrated that the account for the interplane Coulomb interaction enhances the critical temperature of the transition to the superconducting phase.

Kohn-Luttinger superconductivity in monolayer and bilayer semimetals with the Dirac spectrum

The effect of Coulomb interaction in an ensemble of Dirac fermions on the formation of superconducting pairing in monolayer and bilayer doped graphene is studied using the Kohn-Luttinger mechanism disregarding the Van der Waals potential of the substrate and impurities. The electronic structure of graphene is described using the Shubin-Vonsovsky model taking into account the intratomic, interatomic, and interlayer (in the case of bilayer graphene) Coulomb interactions between electrons. The Cooper instability is determined by solving the Bethe-Saltpeter integral equation. The renormalized scattering amplitude is obtained with allowance for the Kohn-Luttinger polarization contributions up to the second order of perturbation theory in the Coulomb interaction. It plays the role of effective interaction in the Bethe-Salpeter integral equation. It is shown that the allowance for the Kohn-Luttinger renormalizations as well as intersite Coulomb interaction noticeably affects the competition between the superconducting phases with the $f-$wave and $d + id-$wave symmetries of the order parameter. It is demonstrated that the superconducting transition temperature for an idealized graphene bilayer with significant interlayer Coulomb interaction between electrons is noticeably higher than in the monolayer case.

Multipole Model for the Electron Group Functions Method

Electron groups provide a natural way to introduce local concepts into quantum chemistry, and the wave functions based on the group products can be considered as a framework for constructing efficient computational methods in terms of "observable" parts of molecular systems. The elements of the group wave functions (electronic structure variables) can be optimized by requiring the number of operations proportional to the size of the molecule. This directly leads to computational methods linearly scaling for large molecular systems. In the present work we consider a particular case of such a wave function implemented for the semiempirical NDDO Hamiltonian. The electron groups are expressed in terms of optimized atomic (hybrid) orbitals with chemical bonds described by geminals and the delocalized groups described by Slater determinants (with or without spin restriction). This scheme is very fast by itself but its speed is considerably limited by the computations of the interatomic Coulomb interactions. Here we develop a consistent method based on group functions which uses the multipole scheme for interatomic interactions. The explicit usage of the atomic multipoles makes the method extremely fast, although the numerical efficiency is largely achieved due to the local character of the electron groups involved. We discuss numerical characteristics of the new method as well as its possible parametrization. We apply this method to study dodecahedral water clusters with hydrogen fluoride substitution and base the analysis on the exhaustive calculation of all symmetry-independent hydrogen-bond networks.

Relative Contributions of Lattice Distortion and Coulomb Interaction to Resonant X-ray Scattering in Manganites

We investigated the origin of the energy splitting observed in the resonant x-ray scattering (RXS) in manganites. Using thin film samples with controlled lattice parameters and orbital states at a fixed orbital filling, we estimated that the contribution of the interatomic Coulomb interaction relative to the Jahn-Teller mechanism is insignificant and at most 0.27. This indicates that RXS probes mainly Jahn-Teller distortion in manganites.

Electronic states, Mott localization, electron-lattice coupling, and dimerization for correlated one-dimensional systems

We discuss physical properties of strongly correlated electron states for a linear chain obtained with the help of the recently proposed new method combining the exact diagonalization in the Fock space with an ab initio readjustment of the single-particle orbitals in the correlated state. The method extends the current discussion of the correlated states since the properties are obtained with varying lattice spacing. The finite system of N atoms evolves with the increasing interatomic distance from a Fermi-liquid-like state into the Mott insulator. The criteria of the localization are discussed in detail since the results are already convergent for N>=8. During this process the Fermi-Dirac distribution gets smeared out, the effective band mass increases by ~50%, and the spin-spin correlation functions reduce to those for the Heisenberg antiferromagnet. Values of the microscopic parameters such as the hopping and the kinetic-exchange integrals, as well as the magnitude of both intra- and inter-atomic Coulomb and exchange interactions are calculated. We also determine the values of various local electron-lattice couplings and show that they are comparable to the kinetic exchange contribution in the strong-correlation limit. The magnitudes of the dimerization and the zero-point motion are also discussed. Our results provide a canonical example of a tractable strongly correlated system with a precise, first-principle description as a function of interatomic distance of a model system involving all hopping integrals, all pair-site interactions, and the exact one-band Wannier functions.

Coulomb energies in alloys

With the help of order-N calculations on realistic models of random substitutional alloys, we have studied the concentration, structure, and composition dependence of the part of the total energy that is stored in the interatomic Coulomb interaction. An observation about the relation between the self-consistent charges associated with a site and the long-range electrostatic potential at the site is used in the analysis.

STRUCTURE AND QUANTUM-SIZE EFFECTS ON THE CHARGING ENERGY OF ALL-METAL ARTIFICIAL ATOMS

The charging and quantum-size effects of all-metal artificial atoms (a tunnel barrier containing a metal particle) are studied by using a Hubbard tight-binding Hamiltonian in the unrestricted Hartree-Fock approximation, which includes intra-atomic and interatomic Coulomb interactions. The charging energy as a function of the electron number added to the artificial atom can be modulated by the artificial atoms is predicted. Furthermore, different charge distributions for the nonequivalent atoms effects of quantum size and structure in the cluster and thus the conductance resonances in all-metal in the artificial atoms are found, which have obvious influence on the electronic transport through all-metal artificial atoms.

The local electronic and magnetic properties of Fe impurity in Al clusters

The local magnetic property,d electronic structure and the charge transfer effect of Fe impurity in Al clusters have been studied by using a tight-binding model Hamiltonian in the unrestricted Hartree-Fock approximation, which includes intra-atomic and interatomic Coulomb interactions. We have obtained that local magnetic moment of Fe impurity in FeAl N clusters decreases with increasing cluster size and convergences to zero (that of bulk given by Anderson) withN larger than 12, meanwhile, the local magnetic moment for smaller clusters depends on the clusters size and it is a monotonous descent function of cluster size. We have also found that the spin splitting of the localizedd states decreases as the cluster size increases, which mainly results from the interaction between the localized electrons of Fe atom and the delocalized electrons of Al atoms.

Charge state formation probabilities of sputtered gold atoms

The yields and the energy spectra of sputtered gold positive and negative ions and atoms are measured. The velocity dependence of the ionization probabilities of sputtered particles is studied. The results obtained are interpreted taking into account the effect of the inter-atomic Coulomb interaction.

Many-body approach to the electronic properties of clusters: Application to doubly charged Pb clusters.

A many-body theoretical approach to the electronic properties of small clusters is presented. The nucleus of the theory is a realistic many-body Hamiltonian with intra-atomic and interatomic Coulomb interactions, which describes the dynamics of the valence electrons. The exact solution and several variational Ansa$iuml---tze (e.g., Hartree-Fock, Gutzwiller) are considered in order to quantify the importance of correlations to the electronic properties. As an application, the stability of doubly charged Pb clusters is studied. From the exact solution of the model we obtain, in agreement with experiment, that ${\mathrm{Pb}}_{3}^{2+}$ has a metastable ground state with isosceles geometry. While the Hartree-Fock approximation fails to account for the metastability, a simple spin-symmetrized Ansatz \ensuremath{\Vert}SSHF〉 yields a very good account of both the geometry and the energy barrier preventing dissociation. One concludes that both the metastability and structure of ${\mathrm{Pb}}_{3}^{2+}$ result mainly from antiferromagnetic quantum spin fluctuations. Furthermore, by introducing local correlations in \ensuremath{\Vert}SSHF〉, more than 99% of the exact binding energy is obtained for the whole range of interatomic distances. General implications and improvements necessary for the study of more complex systems are discussed.

REGULARIZATION OF THE MULTIPOLAR FORM OF QUANTUM ELECTRODYNAMICS

The multipolar form of quantum electrodynamics has been proposed by Power, Zienau et al. It is widely used in nonrelativistic calculations but has the deficiency: its Hamiltonian has a divergent operator term. It is shown that the divergency can be removed by a regularization of the unitary transformation which converts the Coulomb gauge into the multipolar form. The regularized multipolar form is proven to have the same ultraviolet radiative divergencies as the Coulomb gauge electrodynamics. It is also demonstrated that the interaction with soft photons is represented by the usual electric dipole term e qE and interatomic Coulomb interactions persist to be absent.

Study of Electron Correlations in Pb n2+-Clusters

The ground state properties of Pb-clusters are investigated using a many-body Hamiltonian with intra and inter-atomic Coulomb interactions. By solving the model exactly we obtain that Pb is metastable (lifetime τ > 1040s) and that it has isosceles geometry (bondangle Θ ≃ 124°). The importance of electron correlations for the stability of doubly charged clusters is discussed. By comparison between the exact solution and several variational approaches we particularly show that both the metastability and isosceles shape of Pb result mainly from antiferromagnetic quantum spin-fluctuations.

Metastability of Pbn2+ clusters: Role of correlation effects.

The stability of ${\mathrm{Pb}}_{\mathit{n}}^{2+}$ clusters is studied by solving exactly for the valence 6p electrons a realistic many-body Hamiltonian with intratomic and interatomic Coulomb interactions. We obtain that ${\mathrm{Pb}}_{3}^{2+}$ has a metastable ground state and isosceles shape (bond angle \ensuremath{\theta}\ensuremath{\simeq}${124}^{9}$). The energy barrier against dissociation ${\mathit{E}}_{\mathit{B}}$=0.13 eV yields a very long lifetime. This explains the recent experimental observation of ${\mathrm{Pb}}_{3}^{2+}$. Furthermore, comparison with self-consistent Hartree-Fock calculations shows that the metastability of ${\mathrm{Pb}}_{3}^{2+}$ results from electron-correlation effects.

On the stability of Pb n m+ -clusters

The stability of multiply charged Pb n m+ -clusters (n ≤ 3;m=0, 1, 2) was studied by solving exactly for the valencep-electrons a many body Hubbard-like Hamiltonian with intra- and interatomic Coulomb interactions. Particularly we obtain that Pb 3 2+ has a metastable ground state, in which Pb 3 2+ has isosceles shape (bond lengthR=3.2 A, bond angle θ=124°) and a positive binding energyE B =3.4 eV. The activation barrier against dissociation into Pb 2 + + Pb+ is 0.13 eV, yielding a very long lifetime. This is in agreement with recent experiments [1] in which the lifetime of Pb 3 2+ was determined to be at least 10−6 s. Comparison with self consistent Hartree-Fock calculations shows that the metastability of Pb 3 2+ is due to electronic correlations within the paramagnetic ground state.

On the possibility of phase separation in the extended Hubbard model

Abstract The one-band extended Hubbard model on the square lattice in the strong interaction limit is investigated using an exact diagonalization technique. The main emphasis was on the possibility of a phase separation. It is shown that the instability of the system against separation into a no-hole antiferromagnetic phase and an hole-rich phase that takes place at low hole concentrations is effectively destroyed through the inclusion of a moderate interatomic Coulomb interaction. In the two-phase region, i.e. at small interaction energies, a negative hole-binding energy indicates that the hole-rich phase is build up by hole-pairs. We comment on the relevance of our results for the description of the copper-oxide superconductors.

Effective Hamiltonian for High-TcCu Oxides

The effective Hamiltonian for high- T c Cu-based oxide superconductors is derived based on Cu: d x 2 - y 2 and O: p σ orbitals in the Cu–O plane by taking into account the intra- and nearest-neighbor interatomic Coulomb interactions for both cases of hole and electron doping. For hole doping, where the stability of Cu ++ is assumed, the effective Hamiltonian proves to have various interaction processes, some features of which are studied by considering a case with a single Cu spin and one hole in the oxygen band. The spatial extent of the singlet-bound state in this case has been examined to the linear order of the oxygen band width. For electron doping the effective Hamiltonian is much simpler and essentially the same as the t - J model. Based on these results we discuss the relevance of the t - J model to the high- T c Cu oxides. The effects of Cu: d 3 z 2 - r 2 orbitals and O: p z orbitals at the apex of the pyramid or octahedron are also examined.