Claude Ederer

Last Name

Ederer

First Name

Claude

ORCID

0000-0002-2280-8022

Organisational unit

03903 - Spaldin, Nicola A. / Spaldin, Nicola A.

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Publications1 - 10 of 31

Effect of chemical disorder on the magnetic anisotropy in L10 FeNi from first-principles calculations
Si, Mayan; Izardar, Ankit; Ederer, Claude (2022)
Physical Review Research
We use first-principles calculations to investigate how deviations from perfect chemical order affect the magnetocrystalline anisotropy energy (MAE) in L10 FeNi. We first analyze the local chemical environment of the Fe atoms in various partially ordered configurations, using the orbital magnetic moment anisotropy (OMA) as proxy for a local contribution to the MAE. We are able to identify a specific nearest neighbor configuration and use this “favorable environment” to successfully design various structures with MAE higher than the perfectly ordered system. However, a systematic analysis of the correlation between local environment and OMA using smooth overlap of atomic positions indicates only a partial correlation, which exists only if the deviation from full chemical order is not too large, whereas in general no such correlation can be identified even using up to third nearest neighbors. Guided by the observation that the identified favorable environment implies an Fe-rich composition, we investigate the effect of randomly inserting additional Fe into the nominal Ni planes of the perfectly ordered structure. We find that the MAE increases with Fe content, at least up to 62.5% Fe. Thus, our paper shows that the perfectly ordered case is not the one with highest MAE and that an increased MAE can be obtained for slightly Fe-rich compositions.
A new avenue in the search for CP violation: Mössbauer spectroscopy of 227 Ac
Scheck, Marcus; Chapman, Robert; Dobaczewski, Jacek; et al. (2023)
The European Physical Journal A
This work proposes a new avenue in the search for CP-violating odd-electric and even-magnetic nuclear moments. A promising candidate to find such moments in the ground state is the quadrupole-deformed and octupole-correlated nucleus 227-actinium. In this nucleus, the 27.4-keV E1 transition that connects the 3 / 2 + parity-doublet partner and the 3 / 2 - ground state is perfectly suited to apply the sensitive technique of recoil-free selfabsorption, commonly known as Mössbauer spectroscopy. In this experimental approach, the lifetime of the 3 / 2 + upper parity-doublet partner allows an estimate of the lower limit of Δ E= 2 · Γ γ = 23.7 (1) × 10 - 9 eV for the achievable energy resolution to be made. This resolution must be exceeded by the interaction of a CP-violating moment and the corresponding multipole moment of the field distribution in the lattice. This work presents the first ideas for patterns caused by CP-violating moments on the expected quadrupole splitting and nuclear Zeeman effect.
Importance of ligand on-site interactions for the description of Mott-insulators in DFT+DMFT
Carta, Alberto; Panda, Anwesha; Ederer, Claude (2026)
npj Computational Materials
Calculations combining density functional theory (DFT) and dynamical mean-field theory (DMFT) for transition metal (TM) oxides and similar compounds usually focus on improving the description of the TM d states. Here, we emphasize the importance of also accounting for corrections of the ligand p states. We demonstrate that focusing exclusively on improving the description of the TM d states results in difficulties to obtain the correct insulating behavior for a variety of materials, and requires to use values for the local interaction parameters that are inconsistent with values obtained using, e.g., the constrained random phase approximation (cRPA). We demonstrate that, to a large part, these inconsistencies arise from using local/semi-local DFT as starting point for computing interaction parameters, and we show that applying a simple empirical correction to the low energy states not included in the correlated subspace results in improved values for the interaction parameters that then allow to obtain the correct insulating behavior. Moreover, we show that applying an approximate but realistic Hartree-Fock-like correction specifically to the O p orbitals, when they are explicitly included in the DMFT subspace, significantly improves the quantitative accuracy of the DFT+DMFT description for prototypical Mott insulators, including LaTiO3, LaVO3, and the perovskite rare-earth nickelates (RNiO3).
Evidence for Jahn-Teller-driven metal-insulator transition in strained SrCrO3 from first-principles calculations
Carta, Alberto; Ederer, Claude (2022)
Physical Review Materials
Using density-functional theory (DFT) and its extension to DFT + U, we propose a possible scenario for a strain-induced metal-insulator transition which was reported recently in thin films of SrCrO3. The metal-insulator transition involves the emergence of a Jahn-Teller (JT) distortion similar to the case of the related rare-earth vanadates, which also exhibit a nominal d(2) occupation of the transition metal cation. Our calculations indicate that, for realistic values of the Hubbard U parameter, the unstrained system exhibits a C-type antiferromagnetically ordered ground state that is already rather close to a JT instability. However, the emergence of the JT distortion is disfavored by the large energetic overlap of the d(xz)/d(yz) band with the lower-lying d(xy) band. Tensile epitaxial strain lowers the energy of the d(xy) band relative to d(xz)/d(yz) and thus brings the system closer to the nominal filling of d(xy)(1)(d(xz)d(yz))(1). The JT distortion then lifts the degeneracy between the d(xz) and d(yz) orbitals and thus allows the material to open up a gap in the electronic band structure.
Surface Magnetization in Antiferromagnets: Classification, Example Materials, and Relation to Magnetoelectric Responses
Weber, Sophie F.; Urru, Andrea; Bhowal, Sayantika; et al. (2024)
Physical Review X
We use symmetry analysis and density-functional theory to determine and characterize surface terminations that have a finite equilibrium magnetization density in antiferromagnetic materials. A nonzero magnetic dipole moment per unit area or "surface magnetization" can arise on particular surfaces of many antiferromagnets due to the bulk magnetic symmetries. Such surface magnetization underlies intriguing physical phenomena like interfacial magnetic coupling and can be used as a readout method of antiferromagnetic domains. However, a universal description of antiferromagnetic surface magnetization is lacking. We first introduce a classification system based on whether the surface magnetization is either sensitive or robust to roughness and on whether the magnetic dipoles at surface of interest are compensated or uncompensated when the bulk magnetic order is retained at the surface. We show that roughnesssensitive categories can be identified by a simple extension of a previously established group-theory formalism for identifying roughness-robust surface magnetization. We then map the group-theory method of identifying surface magnetization to a novel description in terms of bulk magnetic multipoles, which are already established as symmetry indicators for bulk magnetoelectric responses at both linear and higher orders. We use density-functional calculations to illustrate that nominally compensated surfaces in magnetoelectric Cr2O3 and centrosymmetric altermagnetic FeF2 develop a finite magnetization density at the surface, in agreement with our predictions based on both group theory and the ordering of the bulk multipoles. Our analysis provides a comprehensive basis for understanding the surface magnetic properties and their intimate correspondence to bulk magnetoelectric effects in antiferromagnets and has important implications for technologically relevant phenomena such as exchange-bias coupling.
Calculation of screened Coulomb interaction parameters for the charge-disproportionated insulator CaFeO₃
Merkel, Maximilian Ernest; Ederer, Claude (2024)
Physical Review Research
We calculate the screened electron-electron interaction for the charge-disproportionated insulator CaFeO₃ using the constrained random-phase approximation (cRPA). While in many correlated materials the formation of a Mott-insulating state is driven by a large local Coulomb repulsion, represented by the Hubbard U, several cases have been identified more recently in which U is strongly screened and instead the Hund's interaction J dominates the physics. Our results confirm a strong screening of the local Coulomb repulsion U in CaFeO₃, whereas J is much less screened and can thus stabilize a charge-disproportionated insulating state. This is consistent with the case of the rare-earth nickelates, where similar behavior has been demonstrated. In addition, we validate some common assumptions used for parametrizing the local electron-electron interaction in first-principles calculations based on density-functional theory (DFT), we assess the dependence of the interaction on the choice of correlated orbitals, and we discuss the use of the calculated interaction parameters in DFT+U calculations of CaFeO₃. Our work also highlights certain limitations for the direct use of cRPA results in DFT-based first-principles calculations, in particular for systems with strong entanglement between the correlated and uncorrelated bands.
Interfacial doping in LaVO3/SrVO3 multilayers from DFT+DMFT
Beck, Sophie; Ederer, Claude (2023)
Physical Review Materials
We investigate the effect of spatial doping of the Mott insulator LaVO3 by inserting a few layers of the correlated metal SrVO3 in multilayer geometries. Using DFT in combination with DMFT, we demonstrate that this leads to a geometrically confined and robust metallic layer that stabilizes the metallicity in SrVO3 even in the ultrathin layer limit, suppressing a potential dimensionality-induced metal-insulator transition. For a thicker SrVO3 layer, we find a continuous transition of both structural and electronic properties across the interface between the two materials, with bulk properties reestablished on a length scale of 2to3 unit cells away from the interface. We show that a strain modulation applied along the growth direction can lead to asymmetric charge reconstruction at chemically symmetric interfaces. However, we find that this effect is rather weak, implying that fractional occupancy, and thus metallicity, persists at the interfaces.
Effect of charge self-consistency in DFT+DMFT calculations for complex transition metal oxides
Hampel, Alexander; Beck, Sophie; Ederer, Claude (2020)
Physical Review Research
We investigate the effect of charge self-consistency (CSC) in density-functional theory plus dynamical mean-field theory calculations compared to simpler “one-shot” calculations for materials where interaction effects lead to a strong redistribution of electronic charges between different orbitals or between different sites. We focus on two systems close to a metal-insulator transition (MIT), for which the importance of CSC is currently not well understood. Specifically, we analyze the strain-related orbital polarization in the correlated metal CaVO3 and the spontaneous electronic charge disproportionation in the rare-earth nickelate LuNiO3. In both cases, we find that the CSC treatment reduces the charge redistribution compared to cheaper one-shot calculations. However, while the MIT in CaVO3 is only slightly shifted due to the reduced orbital polarization, the effect of the site polarization on the MIT in LuNiO3 is more subtle. Furthermore, we highlight the role of the double-counting correction in CSC calculations containing different inequivalent sites.
Spectroscopic signatures and origin of hidden order in Ba₂MgReO₆
Soh, Jian-Rui; Merkel, Maximilian Ernest; Pourovskii, Leonid V.; et al. (2024)
Nature Communications
Clarifying the underlying mechanisms that govern ordering transitions in condensed matter systems is crucial for comprehending emergent properties and phenomena. While transitions are often classified as electronically driven or lattice-driven, we present a departure from this conventional picture in the case of the double perovskite Ba2MgReO6. Leveraging resonant and non-resonant elastic x-ray scattering techniques, we unveil the simultaneous ordering of structural distortions and charge quadrupoles at a critical temperature of Tq ~ 33 K. Using a variety of complementary first-principles-based computational techniques, we demonstrate that, while electronic interactions drive the ordering at Tq, it is ultimately the lattice distortions that dictate the specific ground state that emerges. Our findings highlight the crucial interplay between electronic and lattice degrees of freedom, providing a unified framework to understand and predict unconventional emergent phenomena in quantum materials.
Magnetic and ferroelectric properties of Sr1−xBaxMnO3 from first principles
Edström, Alexander; Ederer, Claude (2020)
Physical Review Research
Density functional theory (DFT) calculations are used to study the magnetic and ferroelectric properties of Sr1−xBaxMnO3, with focus on x=0.5, under isotropic volume expansion or compression and biaxial strain. Our results indicate that, unexpectedly, Ba substitution alters the electronic structure in a way that, at fixed lattice parameter, notably enhances the interatomic magnetic exchange interactions. However, increasing Ba content also causes a volume expansion which tends to weaken these interactions, leading to a net effect of weakly suppressed magnetism, as observed in experiments. The ferroelectric properties, on the other hand, are found to be less affected by changes in the electronic structure and can largely be understood in terms of the volume expansion caused by Ba substitution. The calculated electric polarization as a function of biaxial strain in Sr1−xBaxMnO3 for x=0 and x=0.5 shows that the difference between the two is mainly due to differences in the magnetic order at certain strain values, accompanied by enormous magnetoelectric coupling.

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Claude Ederer

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