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 materialspecific theoretical tools with predictive power for spectral probes, i.e., diagonal and offdiagonal conductivities. This will be achieved by performing materialspecific 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 materialspecific predictions on multipartite quantum entanglement through the quantum Fisher information.
Publications
2024 

Jones, D.; Östlin, A.; Weh, A.; Beiuşeanu, F.; Eckern, U.; Vitos, L.; Chioncel, L. Superconducting transition temperatures of pure vanadium and vanadiumtitanium 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 superconductorinsulator 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 vanadiumtitanium alloys. Disorder is modeled using the coherent potential approximation while local electronic interactions are treated using dynamical meanfield 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 concentrationdependent increase of Tc, and its maximal value of about 20%.  
2023 

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 easyplane anisotropy and vortexdomain pattern in the kagome ferromagnet Fe_{3}Sn 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 highquality 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 K1 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 micrometerscale magnetic vortices with weakly pinned cores that vanish at the saturation field of similar to 3T applied perpendicular to the kagome plane. The observed vortexdomain structure is well reproduced by the micromagnetic simulations, using the experimentally determined value of the anisotropy and exchange stiffness. (c) 2023 Author(s). 