Publications by authors named "Silke Biermann"
Article Synopsis
- Understanding the physics of the single-orbital Hubbard model is crucial for grasping how metal-insulator transitions occur in real materials, particularly in the intermediate-coupling regime.
- Recent advanced techniques have helped analyze the spectral function in this intermediate regime, clarifying how antiferromagnetic fluctuations and local electronic correlations contribute to forming an insulating state.
- The study delineates the distinct Slater and Heisenberg regimes of the phase diagram, highlighting a crossover region where competing spatial and local electronic correlations affect the local magnetic moment and the overall insulating state.
Article Synopsis
- Spintronics and orbitronics can benefit from orbital-selective behaviors in correlated electron materials, particularly through phenomena like the orbital-selective Mott state.
- The study investigates the possibility of an orbital-selective Néel transition (OSNT), which involves different magnetic behaviors across orbitals and requires the absence of Hund's exchange coupling.
- Through two-orbital calculations, the research reveals that OSNT can occur across various interaction strengths, with different mechanisms (Slater or Heisenberg) governing the transition depending on the coupling regime.
Article Synopsis
- Characterizing nonlocal magnetic fluctuations in materials with strong electronic interactions is a big challenge in modern condensed matter theory, especially for perovskite materials.
- The authors developed a diagrammatic extension of dynamical mean-field theory and focused on a three-orbital model to explore how magnetic fluctuations behave under different conditions.
- They found that the nature of these fluctuations changes significantly with the strength of Hund's coupling, affecting how spins interact and leading to different orbital behaviors depending on electron filling.
Article Synopsis
- Strong electron repulsion in solids can lead to a phenomenon called the "Mott" metal-to-insulator transition (MIT), where electrons transform from a mobile to a localized state.
- Understanding this transition has been difficult for over 50 years due to challenges in observing both electronic states.
- Researchers used angle-resolved photoemission spectroscopy (ARPES) to demonstrate that in vanadium oxide (VO), increasing temperature causes the itinerant conduction band to vanish while a quasi-localized state shifts to higher binding energies.
Article Synopsis
- 5d iridium oxides, like strontium iridate (Sr₂IrO₄), are being studied for potential new quantum states due to strong spin-orbit coupling and an unconventional Mott insulating state.
- Researchers used polarized neutron diffraction to measure the magnetization density in Sr₂IrO₄, revealing that its distribution is anisotropic and aspherical, differing from the expected j_{eff}=1/2 model.
- The study found that the magnetization density showed a dominant xy orbital contribution, suggesting that the relationship to superconducting copper oxides may not be as strong as previously believed.
Article Synopsis
- - The study addresses a key challenge in calculating effective Coulomb interactions in low-energy Hamiltonians for materials with strong electronic correlations, which typically complicates fully parameter-free electronic structure calculations.
- - A new method is proposed to determine effective local Coulomb interactions specifically for charge-transfer oxides, factoring in intershell interactions that effectively reduce local interactions on the correlated shell.
- - This new approach helps clarify inconsistencies in existing methods for calculating effective interactions across various materials and enhances the understanding of how cluster models relate to dynamical mean field theories in electronic structure calculations.
Stabilizing superconductivity at high temperatures and elucidating its mechanism have long been major challenges of materials research in condensed matter physics. Meanwhile, recent progress in nanostructuring offers unprecedented possibilities for designing novel functionalities. Above all, thin films of cuprate and iron-based high-temperature superconductors exhibit remarkably better superconducting characteristics (for example, higher critical temperatures) than in the bulk, but the underlying mechanism is still not understood.
View Article and Find Full Text PDFArticle Synopsis
- Understanding the Fermi surface and low-energy excitations of iron or cobalt pnictides is important for studying electronic instabilities like magnetism and superconductivity.
- The authors introduce a new method to analyze low-energy properties in correlated electron materials, incorporating advanced screening effects and local dynamical correlations.
- This approach successfully clarifies the inconsistency in the behavior of BaCo2As2, which traditional methods predicted to show a ferromagnetic instability that isn't observed experimentally.
Article Synopsis
- The text introduces dynamical mean field approaches, emphasizing the need to understand electronic correlations in materials beyond traditional band theory.
- It discusses the fundamentals of dynamical mean field theory (DMFT) and showcases its application in realistic electronic structure calculations, using examples from transition metals and rare-earth compounds.
- Lastly, it highlights recent advancements in calculating effective Hubbard interactions and understanding dynamical screening effects in solids.
Article Synopsis
- The text summarizes advancements in electronic structure calculations for materials that exhibit strong electronic Coulomb correlations, focusing on updates beyond the established LDA + DMFT framework.
- It highlights the importance of dynamical screening effects in solids, which lead to frequency-dependent local Coulomb interactions (U(ω)), crucial for accurate first principles descriptions.
- The review discusses the newly introduced LDA + U(ω) + DMFT method and the GW + DMFT scheme, showcasing recent calculations and their applications to specific materials and systems, while also exploring future prospects in the field.
What about U on surfaces? Extended Hubbard models for adatom systems from first principles.
J Phys Condens Matter
March 2013
Article Synopsis
- Electronic correlations and dimensional constraints significantly impact the properties of semiconductor surfaces and adatom systems, making them a focus in condensed matter physics research.
- Current theoretical studies are lacking in terms of accounting for many-body effects and often treat inter-electronic interactions as adjustable parameters rather than deriving them from first principles.
- The researchers have calculated the inter-electronic Coulomb interactions for group IV surface-adatom systems on Si(111) and developed an extended Hubbard model to facilitate future many-body calculations, revealing substantial interactions that are crucial to understanding these systems.
We present a fully self-consistent combined GW and dynamical mean field (DMFT) study of the extended two-dimensional Hubbard model. The inclusion of the local dynamical vertex stemming from the DMFT self-energy and polarization is shown to cure the known problems of self-consistent GW. We calculate momentum-resolved spectral functions, two-particle polarizations, and electron-loss spectra, as well as the effective dynamical interaction induced by nonlocal screening.
View Article and Find Full Text PDFRare-earth vs. heavy metal pigments and their colors from first principles.
Proc Natl Acad Sci U S A
January 2013
Article Synopsis
- Many inorganic pigments, often containing harmful heavy metals, are being replaced with nontoxic alternatives derived from rare-earth elements, but understanding their color properties is complex.
- This study focuses on computing the colors of cerium fluorosulfide and mercury sulfide pigments using advanced computational techniques that consider optical absorption and how factors like film thickness and pigment concentration impact coloration.
- The findings reveal that while mercury sulfide meets performance criteria due to its wide band transitions, cerium fluorosulfide achieves its bright red color through a unique combination of quasi-2D states and localized properties, showcasing the potential of computational methods in designing materials with specific optical characteristics.
Article Synopsis
- * A combination of advanced theoretical methods reveals that strong spin-orbit interactions, along with structural distortions, lead to a suppression of spin-orbital fluctuations.
- * Findings indicate that Sr(2)IrO(4) behaves as a paramagnetic spin-orbitally ordered Mott insulator at room temperature, while Sr(2)RhO(4) remains metallic, and our theoretical spectra align well with experimental photoemission results.
Generalized Hedin equations and σGσW approximation for quantum many-body systems with spin-dependent interactions.
J Phys Condens Matter
February 2009
The Hedin equations for the electron self-energy and the vertex were originally derived for a many-electron system with Coulomb interaction (Hedin 1965 Phys. Rev. 139 A796).
View Article and Find Full Text PDFMulti-orbital effects in optical properties of vanadium sesquioxide.
J Phys Condens Matter
February 2009
Vanadium sesquioxide, V(2)O(3), boasts a rich phase diagram whose description necessitates accounting for many-body Coulomb correlations. The spectral properties of this compound have been successfully addressed within dynamical mean field theory to the extent that results of recent angle-resolved photoemission experiments have been correctly predicted. While photoemission spectroscopy probes the occupied part of the one-particle spectrum, optical experiments measure transitions into empty states and thus provide complementary information.
View Article and Find Full Text PDFEffective band structure of correlated materials: the case of VO(2).
J Phys Condens Matter
September 2007
Article Synopsis
- - Vanadium dioxide (VO(2)) exhibits a metal-insulator transition at 340 K, raising debates about whether the insulating phase is influenced more by electron correlation (Mott) or lattice distortion (Peierls) effects.
- - Recent research suggests that this transition is a mix of the two, termed correlation-assisted Peierls, with new calculations focusing on the excitation spectrum of the insulating M1 phase.
- - The study finds that in the M1 phase, strong interactions have minimal effects on particle lifetimes, allowing for a simplified band structure description, confirmed through analytic methods that help determine the behavior of electron bands during the transition.
Article Synopsis
- The study explores the metal-to-insulator transition (MIT) in BaVS3 using advanced theoretical methods, specifically dynamical mean-field theory and density functional theory.
- It reveals that correlation effects cause a significant redistribution of charge, which changes the occupancy levels between different energy bands and alters the Fermi surface.
- This research addresses inconsistencies between theoretical band predictions and experimental results, clarifying aspects like the charge-density-wave ordering vector and the emergence of local moments in the metallic state.