A5: Optical conductivities and entanglement in magnetic topological semimetals
Liviu Chioncel, Markus Heyl
In this project we study a variety of topological materials from the family of the Kagome magnets which are relevant for the experimental efforts of the overall project. In this context our aim is twofold. First, we plan to develop and apply material-specific theoretical tools with predictive power for spectral probes, i.e., diagonal and off-diagonal conductivities. This will be achieved by performing material-specific as well as model calculations combining Density Functional Theory with many body physics using Dynamical Mean Field Theory and its cluster extensions. Second, we aim to use these methods in order to make material-specific predictions on multipartite quantum entanglement through the quantum Fisher information.
Publications
2025 |
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Sharma, S.; Chioncel, L.; Marco, I. Di Exploring strong electronic correlations in the breathing kagome metal Fe3Sn Journal Article Phys. Rev. B 111, 235127 (2025). @article{sharma_exploring_2025,Kagome metals have emerged as pivotal materials in condensed matter physics due to their unique geometric arrangement and intriguing electronic properties. Understanding the origin of magnetism in these materials, particularly in iron-rich Fe-Sn binary compounds such as Fe3Sn, holds a significant importance, as they represent potential candidates for permanent magnets with a high Curie temperature and a strong magnetic anisotropy. In the present study, we employ density functional theory and dynamical mean-field theory to analyze the electronic structure and magnetic properties of Fe3Sn. Our investigation reveals the presence of several nearly flat bands and Weyl nodes at low excitation energies. The inclusion of local correlation effects is shown to push these features even closer to the Fermi energy, which may be important for their manipulation via external stimuli. Regarding magnetism, the Hubbard-like interaction leads to an increase of orbital polarization at the expenses of a minor reduction of the spin moment. The magnetic anisotropy energy exhibits a strong dependence on the particular choice of the Coulomb interaction parameters. Additionally, our detailed analysis of the interatomic exchange interactions indicates a significant contribution from the antisymmetric exchange, i.e., the Dzyaloshinskii-Moriya interaction, which showcases the existence of magnetic chirality in the system. Overall, our investigation highlights a strong interplay between the flat bands near the Fermi level, the local Coulomb interaction, and the triangular geometry of the lattice, which plays a crucial role in driving the magnetic properties of this material. |  |
2024 |
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Prodan, L.; Chmeruk, A.; Chioncel, L.; Tsurkan, V.; Kézsmárki, I. Anisotropic charge transport in the easy-plane kagome ferromagnet Fe3Sn Journal Article Phys. Rev. B 110, 094407 (2024). @article{prodan_anisotropic_2024,We report on the anisotropic electronic properties of the metallic kagome ferromagnet , as revealed by magnetotransport studies on single-crystalline samples and material-specific ab initio calculations. The longitudinal resistivity shows a remarkable anisotropy, where surprisingly the resistivity perpendicular to the kagome planes is about three times lower than the in-plane resistivity (𝜌𝑥𝑥). The ordinary Hall constants are negative for the magnetic field applied parallel to the 𝐇||𝐜 and positive for 𝐇||𝐚, indicating the coexistence of electron- and hole-like carriers at the Fermi surface. The anomalous Hall resistivity (𝜌𝐴𝑖𝑗) shows large values over a wide temperature range and exhibits a significant anisotropy ratio (𝜌𝑥𝑦/𝜌𝑧𝑦), with 𝜌𝑥𝑦 =8 µΩcm and 𝜌𝑧𝑦 =3.2 µΩcm at room temperature. Our study reveals that the anisotropy ratio scales almost linearly with the magnetocrystalline anisotropy constant (𝐾𝑢) over a broad temperature range (2 K ≤ T ≤ 300 K), indicating that spin-orbit coupling is the underlying mechanism driving both the anisotropic transport properties and the magnetocrystalline anisotropy energy. Material-specific ab initio calculations further demonstrate that the magnetic reconstruction of bands near the Fermi level, induced by the spin-orbit coupling, is predominantly responsible for the anisotropic behavior of the Berry curvature and, consequently, the large anomalous Hall effect observed in Fe3Sn. These results provide valuable insight into the complex interplay between charge transport and magnetism in kagome magnets, emphasizing the strong manifestation of spin-orbit coupling on kagome lattices. | |
Jones, D.; Östlin, A.; Weh, A.; Beiuşeanu, F.; Eckern, U.; Vitos, L.; Chioncel, L. Superconducting transition temperatures of pure vanadium and vanadium-titanium alloys in the presence of dynamical electronic correlations Journal Article Phys. Rev. B 109, 165107 (2024). @article{jones_superconducting_2024,Ordinary superconductors are widely assumed insensitive to small concentrations of random nonmagnetic impurities, whereas strong disorder suppresses superconductivity, ultimately leading to a superconductor-insulator transition. In between these limiting cases, a most fascinating regime may emerge where disorder enhances superconductivity. This effect is discussed here for the β phase of vanadium-titanium alloys. Disorder is modeled using the coherent potential approximation while local electronic interactions are treated using dynamical mean-field theory. The McMillan formula is employed to estimate the superconducting transition temperature, showing a maximum at a Ti concentration of around 0.33 for a local Coulomb interaction U in the range of 2 eV to 3 eV. Our calculations quantitatively agree with the experimentally observed concentration-dependent increase of Tc, and its maximal value of about 20%. | |
2023 |
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Prodan, L.; Evans, D. M.; Griffin, S. M.; Oestlin, A.; Altthaler, M.; Lysne, E.; Filippova, I. G.; Shova, S.; Chioncel, L.; Tsurkan, V.; Kézsmárki, I. Large ordered moment with strong easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe3Sn Journal Article Appl. Phys. Lett. 123, 021901 (2023). @article{prodan_large_2023,We report the magnetic anisotropy of kagome bilayer ferromagnet Fe3Sn probed by the bulk magnetometry and magnetic force microscopy (MFM) on high-quality single crystals. The dependence of magnetization on the orientation of the external magnetic field reveals strong easyplane magnetocrystalline anisotropy and anisotropy of the saturation magnetization. The leading magnetocrystalline anisotropy constant shows a monotonous increase from K-1 approximate to -1.0 x 10(6) J/m(3) at 300K to -1.3 x 10(6) J/m(3) at 2K. Our ab initio electronic structure calculations yield the value of total magnetic moment of 7.1 mu(B)=f.u. and a magnetocrystalline anisotropy energy density of -0.57meV=f.u. (-1.62 x 10(6)J/m(3)) both being in reasonable agreement with the experimental values. The MFM imaging reveals micrometer-scale magnetic vortices with weakly pinned cores that vanish at the saturation field of similar to 3T applied perpendicular to the kagome plane. The observed vortex-domain structure is well reproduced by the micromagnetic simulations, using the experimentally determined value of the anisotropy and exchange stiffness. (c) 2023 Author(s). | |