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Balazs Ujfalussy

Bio: Balazs Ujfalussy is an academic researcher from Hungarian Academy of Sciences. The author has contributed to research in topics: Magnetic anisotropy & Magnetization. The author has an hindex of 21, co-authored 77 publications receiving 1535 citations. Previous affiliations of Balazs Ujfalussy include Vienna University of Technology & University of Tennessee.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a conceptually clear and transparent derivation of the real-space screened Korringa-Kohn-Rostoker method is presented within the framework of the generalized multiple-scattering theory.
Abstract: Within the framework of the generalized multiple-scattering theory, a conceptually clear and transparent derivation of the real-space screened Korringa-Kohn-Rostoker method is presented. It is suggested that, by a suitable choice of the reference system, a fast exponential spatial decay of the structure constants can be obtained. This opens the way to treat large-scale systems in real space with a computational complexity that scales more favorably than the usual increase with the third power of the number of atoms.

218 citations

Journal ArticleDOI
TL;DR: In this paper, the spin-polarized fully relativistic version of the screened Korringa-Kohn-Rostoker method for semi-infinite systems is presented.
Abstract: In order to treat the orientation of the magnetic field at surfaces properly, the spin-polarized fully relativistic version of the screened Korringa-Kohn-Rostoker method for semi-infinite systems is presented. Magnetic anisotropy energies up to six iron layers on Au(001) are calculated by using the force theorem, predicting a change from a perpendicular to a parallel magnetization for a layer thickness between three and four layers of Fe, in very good agreement with experimental observations. In particular, the magnetic anisotropy energy is discussed in relation to the orbital magnetic moment and to the orientation of the magnetic field when changed continuously.

144 citations

Journal ArticleDOI
TL;DR: A Green's-function technique is presented that describes the electronic properties of surfaces and interfaces in the framework of multiple-scattering theory as based on localized structure constants.
Abstract: A Green's-function technique is presented that describes the electronic properties of surfaces and interfaces in the framework of multiple-scattering theory as based on localized structure constants Results of self-consistent calculations are presented for the Cu (111), (110), and (100) surfaces The obtained surface densities of states and work functions are in good agreement with previous calculations

141 citations

Journal ArticleDOI
TL;DR: In this article, the authors used k⋅p perturbation theory with a simple group-theoretical analysis and constructed effective Rashba Hamiltonians for different point groups up to third order in the wave number.
Abstract: In order to explain the anisotropic Rashba-Bychkov effect observed in several metallic-surface-state systems, we use k⋅p perturbation theory with a simple group-theoretical analysis and construct effective Rashba Hamiltonians for different point groups up to third order in the wave number. We perform relativistic ab initio calculations for the (3√×3√)R30∘ Bi/Ag(111) surface alloy, and from the calculated splitting of the band dispersion we find evidence of the predicted third-order terms. Furthermore, we derive expressions for the corresponding third-order Rashba parameters to provide a simple explanation of the qualitative difference concerning the Rashba-Bychkov splitting of the surface states at Au(111) and Bi/Ag(111).

103 citations

Journal ArticleDOI
TL;DR: This paper presents a meta-analyses of the chiral stationary phase transition of the response of the Higgs boson to the E-modulus of the electron.
Abstract: We perform fully relativistic spin-polarized local spin density calculations for Au covered Co monolayer on Au(111). In accord with a trend observed in experiments we obtain an enhancement of perpendicular magnetic anisotropy as a function of the Au coverage. The close relationship found between the anisotropies of orbital magnetic moments and the anisotropy energies leads to an interpretation of our results in terms of familiar perturbation theory. By using this framework the anomalous behavior of the magnetic anisotropy energies can be well explained due to changes in the sp-d hybridization at the interface of Co monolayer and Au cap.

101 citations


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Book
01 Jan 2004
TL;DR: In this paper, the Kohn-Sham ansatz is used to solve the problem of determining the electronic structure of atoms, and the three basic methods for determining electronic structure are presented.
Abstract: Preface Acknowledgements Notation Part I. Overview and Background Topics: 1. Introduction 2. Overview 3. Theoretical background 4. Periodic solids and electron bands 5. Uniform electron gas and simple metals Part II. Density Functional Theory: 6. Density functional theory: foundations 7. The Kohn-Sham ansatz 8. Functionals for exchange and correlation 9. Solving the Kohn-Sham equations Part III. Important Preliminaries on Atoms: 10. Electronic structure of atoms 11. Pseudopotentials Part IV. Determination of Electronic Structure, The Three Basic Methods: 12. Plane waves and grids: basics 13. Plane waves and grids: full calculations 14. Localized orbitals: tight binding 15. Localized orbitals: full calculations 16. Augmented functions: APW, KKR, MTO 17. Augmented functions: linear methods Part V. Predicting Properties of Matter from Electronic Structure - Recent Developments: 18. Quantum molecular dynamics (QMD) 19. Response functions: photons, magnons ... 20. Excitation spectra and optical properties 21. Wannier functions 22. Polarization, localization and Berry's phases 23. Locality and linear scaling O (N) methods 24. Where to find more Appendixes References Index.

2,690 citations

Journal ArticleDOI
TL;DR: In this article, a review of the basic ideas and techniques of spectral density functional theory which are currently used in electronic structure calculations of strongly correlated materials where the one-dimensional electron description breaks down is presented.
Abstract: We present a review of the basic ideas and techniques of the spectral density functional theory which are currently used in electronic structure calculations of strongly{correlated materials where the one{electron description breaks down. We illustrate the method with several examples where interactions play a dominant role: systems near metal{insulator transition, systems near volume collapse transition, and systems with local moments.

1,921 citations

Journal ArticleDOI
TL;DR: In this paper, a comprehensive survey of experimental studies on the magnetic anisotropy in metallic multilayers containing Fe, Co or Ni is presented and commented on, with the help of some dedicated experimental studies.
Abstract: Ferromagnetic materials exhibit intrinsic `easy' and `hard' directions of the magnetization. This magnetic anisotropy is, from both a technological and fundamental viewpoint one of the most important properties of magnetic materials. The magnetic anisotropy in metallic magnetic multilayers forms the subject of this review article. As individual layers in a multilayer stack become thinner, the role of interfaces and surfaces may dominate that of the bulk: this is the case in many magnetic multilayers, where a perpendicular interface contribution to the magnetic anisotropy is capable of rotating the easy magnetization direction from in the film plane to perpendicular to the film plane. In this review, we show that the (in-plane) volume and (perpendicular) interface contribution to the magnetic anisotropy have been separated into terms related to mechanical stresses, crystallographic structure and the planar shape of the films. In addition, the effect of roughness, often inherent to the deposition techniques used, has been addressed theoretically. Several techniques to prepare multilayers and to characterize their growth as well as methods to determine the magnetic anisotropy are discussed. A comprehensive survey of experimental studies on the perpendicular magnetic anisotropy in metallic multilayers containing Fe, Co or Ni is presented and commented on. Two major subjects of this review are the extrinsic effects of strain, roughness and interdiffusion and the intrinsic effect of the crystallographic orientation on the magnetic anisotropy. Both effects are investigated with the help of some dedicated experimental studies. The results of the orientational dependence studies are compared with ab initio calculations. Finally, the perpendicular surface anisotropy and the in-plane step anisotropy are discussed.

1,099 citations

Journal ArticleDOI
01 Jan 1906

935 citations

Journal Article
TL;DR: High-resolution spectroscopic imaging techniques show that the onset of superconductivity, which gaps the electronic density of states in the bulk of the Fe chains, is accompanied by the appearance of zero-energy end-states, providing strong evidence for the formation of a topological phase and edge-bound Majorana fermions in atomic chains.
Abstract: A possible sighting of Majorana states Nearly 80 years ago, the Italian physicist Ettore Majorana proposed the existence of an unusual type of particle that is its own antiparticle, the so-called Majorana fermion. The search for a free Majorana fermion has so far been unsuccessful, but bound Majorana-like collective excitations may exist in certain exotic superconductors. Nadj-Perge et al. created such a topological superconductor by depositing iron atoms onto the surface of superconducting lead, forming atomic chains (see the Perspective by Lee). They then used a scanning tunneling microscope to observe enhanced conductance at the ends of these chains at zero energy, where theory predicts Majorana states should appear. Science, this issue p. 602; see also p. 547 Scanning tunneling microscopy is used to observe signatures of Majorana states at the ends of iron atom chains. [Also see Perspective by Lee] Majorana fermions are predicted to localize at the edge of a topological superconductor, a state of matter that can form when a ferromagnetic system is placed in proximity to a conventional superconductor with strong spin-orbit interaction. With the goal of realizing a one-dimensional topological superconductor, we have fabricated ferromagnetic iron (Fe) atomic chains on the surface of superconducting lead (Pb). Using high-resolution spectroscopic imaging techniques, we show that the onset of superconductivity, which gaps the electronic density of states in the bulk of the Fe chains, is accompanied by the appearance of zero-energy end-states. This spatially resolved signature provides strong evidence, corroborated by other observations, for the formation of a topological phase and edge-bound Majorana fermions in our atomic chains.

877 citations