| 1. |
- Galler, Anna, et al.
(author)
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Towards ab initio Calculations with the Dynamical Vertex Approximation
- 2018
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In: Journal of the Physical Society of Japan. - : PHYSICAL SOC JAPAN. - 0031-9015 .- 1347-4073. ; 87:4
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Journal article (peer-reviewed)abstract
- While key effects of the many-body problem-such as Kondo and Mott physics-can be understood in terms of onsite correlations, non-local fluctuations of charge, spin, and pairing amplitudes are at the heart of the most fascinating and unresolved phenomena in condensed matter physics. Here, we review recent progress in diagrammatic extensions to dynamical mean-field theory for ab initio materials calculations. We first recapitulate the quantum field theoretical background behind the two-particle vertex. Next we discuss latest algorithmic advances in quantum Monte Carlo simulations for calculating such two-particle quantities using worm sampling and vertex asymptotics, before giving an introduction to the ab initio dynamical vertex approximation (AbinitioDGA). Finally, we highlight the potential of AbinitioDGA by detailing results for the prototypical correlated metal SrVO3.
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| 2. |
- Jonsson, Viktor, et al.
(author)
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Photoelectron dispersion in metallic and insulating thin films
- 2021
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In: Physical Review Research. - : American Physical Society. - 2643-1564. ; 3:3
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Journal article (peer-reviewed)abstract
- The underlying mechanism behind the metal-to-insulator transition in is still a topic of intense debate. The two leading theoretical interpretations associate the transition with either electron-lattice or electron-electron correlations. Novel experimental results are required to converge towards one of the two scenarios. Here we report on a temperature-dependent angle-resolved photoelectron study of thin films across the metal-to-insulator transition. The obtained experimental results are compared to density functional theory calculations. We find an overall energy shift and compression of the electronic band structure across the transition while the overall band topology is conserved. The results demonstrate the importance of electron-electron correlations in establishing the insulating state.
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| 3. |
- Björnson, Kristofer, et al.
(author)
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In Situ Pseudopotentials for Electronic Structure Theory
- 2021
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 15103-15111
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Journal article (peer-reviewed)abstract
- We present a general method of constructing in situ pseodopotentials from first-principles, all-electron, and full-potential electronic structure calculations of a solid. The method is applied to bcc Na, at low-temperature equilibrium volume. The essential steps of the method involve (i) calculating an all-electron Kohn-Sham eigenstate, (ii) replacing the oscillating part of the wave function (inside the muffin-tin spheres) of this state, with a smooth function, (iii) representing the smooth wave function in a Fourier series, and (iv) inverting the Kohn-Sham equation, to extract the pseudopotential that produces the state generated in steps i-iii. It is shown that an in situ pseudopotential can reproduce an all-electron full-potential eigenvalue up to the sixth significant digit. A comparison of the all-electron theory, in situ pseudopotential theory, and the standard nonlocal pseudopotential theory demonstrates good agreement, e.g., in the energy dispersion of the 3s band state of bcc Na.
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| 4. |
- Borisov, Vladislav, et al.
(author)
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Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spin-orbit coupling
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:17
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Journal article (peer-reviewed)abstract
- The Dzyaloshinskii-Moriya (DM) interaction, as well as symmetric anisotropic exchange, are important ingredients for stabilizing topologically nontrivial magnetic textures, such as, e.g., skyrmions, merons, and hopfions. These types of textures are currently in focus from a fundamental science perspective and they are also discussed in the context of future spintronics information technology. While the theoretical understanding of the Heisenberg exchange interactions is well developed, it is still a challenge to access, from first principles theory, the DM interaction as well as the symmetric anisotropic exchange, which both require a fully-relativistic treatment of the electronic structure, in magnetic systems where substantial electron-electron correlations are present. Here, we present results of a theoretical framework which allows to compute these interactions in any given system and demonstrate its performance for several selected cases, for both bulk and low-dimensional systems. We address several representative cases, including the bulk systems CoPt and FePt, the B20 compounds MnSi and FeGe as well as the low-dimensional transition metal bilayers Co/Pt(111) andMn/W(001). The effect of electron-electron correlations is analyzed using dynamical mean-field theory on the level of the spin-polarized T -matrix + fluctuating exchange (SPTF) approximation, as regards the strength and character of the isotropic (Heisenberg) and anisotropic (DM) interactions in relation to the underlying electronic structure. Our method can be combined with more advanced techniques for treating correlations, e.g., quantum Monte Carlo and exact diagonalization methods for the impurity solver of dynamical mean-field theory. We find that correlation-induced changes of the DM interaction can be rather significant, with up to fivefold modifications in the most distinctive case.
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| 7. |
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| 8. |
- Galler, Anna, et al.
(author)
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Orbital and electronic entanglement in quantum teleportation schemes
- 2021
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In: Physical Review Research. - : American Physical Society. - 2643-1564. ; 3:3
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Journal article (peer-reviewed)abstract
- With progress toward more compact quantum computing architectures, fundamental questions regarding the entanglement of indistinguishable particles need to be addressed. In a solid state device, this quest is naturally connected to the quantum correlations of electrons. Here, we analyze the formation of orbital (mode) and particle entanglement in strongly correlated materials due to the Coulomb interaction between the electrons. We extend the analysis to include spectroscopic measurements of the electronic structure, with a particular focus on the photoemission process. To study the role of the different forms of electronic entanglement, including the effect of particle-number superselection rules, we propose and analyze three different electronic teleportation schemes: quantum teleportation within (i) a molecule on graphene, (ii) a nitrogen-vacancy center, and (iii) a quantum dot array.
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| 9. |
- Galler, Anna, et al.
(author)
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The AbinitioD Gamma A Project v1.0 : Non-local correlations beyond and susceptibilities within dynamical mean-field theory
- 2019
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In: Computer Physics Communications. - : ELSEVIER. - 0010-4655 .- 1879-2944. ; 245
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Journal article (peer-reviewed)abstract
- The ab initio extension of the dynamical vertex approximation (D Gamma A) method allows for realistic materials calculations that include non-local correlations beyond GW and dynamical mean-field theory. Here, we discuss the AbinitioD Gamma A algorithm, its implementation and usage in detail, and make the program package available to the scientific community.Program summary: Program Title: AbinitioD Gamma A Program Files: doi: http : //dx doi org/10 17632/h3k3f g6szb. 1 Licensing provisions: GNU General Public License v3 Programming language: Fortran95 and Python Required dependencies: MPI, LAPACK, BLAS, HDF5 (>= 1.8.12), Python (> 2.7), h5py (>= 2.5.0), numpy (>= 1.9.1) Optional dependencies: pip, matplotlib (>= 1.5.1), scipy (>= 0.14.0) Supplementary material: Test case files and step-by-step instructions. Nature of problem: Realistic materials calculations including non-local correlations beyond dynamical mean-field theory (DMFT) as well as non-local interactions. Solving the Bethe-Salpeter equation for multiple orbitals. Determining momentum-resolved susceptibilities in DMFT.Solution method: Ab initio dynamical vertex approximation: starting from the local two-particle vertex and constructing from it the local DMFT correlations, the GW diagrams, and further non-local correlations, e.g., spin fluctuations. Efficient solution of the Bethe-Salpeter equation, avoiding divergencies in the irreducible vertex in the particle-hole channel by reformulating the problem in terms of the full vertex. Parallelization with respect to the bosonic frequency and transferred momentum. Additional comments including restrictions and unusual features: As input, a Hamiltonian derived, e.g., from density functional theory and a DM Gamma T solution thereof is needed including a local two-particle vertex calculated at DMFT self-consistency. Hitherto the AbinitioD Gamma A program package is restricted to SU(2) symmetric problems. A so-called lambda correction or self-consistency is not yet implemented in the AbinitioD Gamma A code. Susceptibilities are so far only calculated within DM Gamma T, not the dynamical vertex approximation.
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| 10. |
- Ghosh, Anirudha, et al.
(author)
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Magnetic circular dichroism in the dd excitation in the van der Waals magnet CrI3 probed by resonant inelastic x-ray scattering
- 2023
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In: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 107:11
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Journal article (peer-reviewed)abstract
- We report on a combined experimental and theoretical study on CrI3 single crystals by employing the polarization dependence of resonant inelastic x-ray scattering (RIXS). Our investigations reveal multiple Cr 3d orbital splitting (dd excitations) as well as magnetic dichroism (MD) in the RIXS spectra. The dd excitation energies are similar on the two sides of the ferromagnetic transition temperature, T-C similar to 61 K, although MD in RIXS is predominant at 0.4 T magnetic field below TC. This demonstrates that the ferromagnetic superexchange interaction that is responsible for the interatomic exchange field is vanishingly small compared with the local exchange field that comes from exchange and correlation interaction among the interacting Cr 3d orbitals. The recorded RIXS spectra reported here reveal clearly resolved Cr 3d intraorbital dd excitations that represent transitions between electronic levels that are heavily influenced by dynamic correlations and multiconfiguration effects. Our calculations taking into account the Cr 3d hybridization with the ligand valence states and the full multiplet structure due to intra-atomic and crystal field interactions in Oh and D3d symmetry clearly reproduced the dichroic trend in experimental RIXS spectra.
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