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2026
Lamp, M.; Ebad-Allah, J.; Chmeruk, A.; Bura, N.; Schönemann, R.; Balicas, L.; Lee, S. H.; Mao, Z. Q.; Chioncel, L.; Kuntscher, C. A. Charge dynamics in the Weyl semimetals NbIrTe₄ and TaIrTe₄ under pressure: Signatures of an electronic phase transition Unpublished (2026), arXiv:2606.02085. Abstract \| Links \| BibTeX \| Project(s): A1, A5 @unpublished{lamp:ChargeDynamics2026, title = {Charge dynamics in the Weyl semimetals NbIrTe_{4} and TaIrTe_{4} under pressure: Signatures of an electronic phase transition}, author = {M. Lamp and J. Ebad-Allah and A. Chmeruk and N. Bura and R. Schönemann and L. Balicas and S. H. Lee and Z. Q. Mao and L. Chioncel and C. A. Kuntscher}, url = {https://arxiv.org/abs/2606.02085}, doi = {10.48550/arXiv.2606.02085}, year = {2026}, date = {2026-06-01}, urldate = {2026-06-01}, abstract = {A high-pressure investigation of the Weyl semimetals NbIrTe4 and TaIrTe4 is presented, using infrared spectroscopy supplemented by density functional theory calculations. The experimental optical conductivity spectra as a function of pressure suggest the occurrence of a pressure-induced phase transition at a critical pressure P_c = 7-8 GPa. This transition is most likely electronic in nature, as Raman scattering measurements provide no evidence of a significant structural phase transition. Above P_c a significant redistribution of spectral weight occurs in the optical conductivity spectrum for both materials. A Drude-Lorentz analysis of the optical data indicates a sharp reduction in the free carrier concentration at P_c, concomitant with the appearance of a low-energy phonon, which was initially screened by free charge carriers. A predominantly electronic origin of the phase transition is supported by the calculated electronic band structure, Fermi surface, and interband optical conductivity as a function of pressure. Our findings provide collective evidence for a pressure-induced, most likely electronic phase transition in both van der Waals materials at P_c=7-8 GPa, highlighting the tunability of their electronic band structure by hydrostatic pressure.}, note = { arXiv:2606.02085}, keywords = {A1, A5}, pubstate = {published}, tppubtype = {unpublished} } Close A high-pressure investigation of the Weyl semimetals NbIrTe4 and TaIrTe4 is presented, using infrared spectroscopy supplemented by density functional theory calculations. The experimental optical conductivity spectra as a function of pressure suggest the occurrence of a pressure-induced phase transition at a critical pressure P_c = 7-8 GPa. This transition is most likely electronic in nature, as Raman scattering measurements provide no evidence of a significant structural phase transition. Above P_c a significant redistribution of spectral weight occurs in the optical conductivity spectrum for both materials. A Drude-Lorentz analysis of the optical data indicates a sharp reduction in the free carrier concentration at P_c, concomitant with the appearance of a low-energy phonon, which was initially screened by free charge carriers. A predominantly electronic origin of the phase transition is supported by the calculated electronic band structure, Fermi surface, and interband optical conductivity as a function of pressure. Our findings provide collective evidence for a pressure-induced, most likely electronic phase transition in both van der Waals materials at P_c=7-8 GPa, highlighting the tunability of their electronic band structure by hydrostatic pressure. Close https://arxiv.org/abs/2606.02085 doi:10.48550/arXiv.2606.02085 Close
2025
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). Abstract \| Links \| BibTeX \| Project(s): A5 @article{sharma_exploring_2025, title = {Exploring strong electronic correlations in the breathing kagome metal Fe_{3}Sn}, author = {S. Sharma and L. Chioncel and I. Di Marco}, url = {https://link.aps.org/doi/10.1103/xmmr-mfv4}, doi = {10.1103/xmmr-mfv4}, year = {2025}, date = {2025-06-16}, urldate = {2025-06-16}, journal = {Phys. Rev. B}, volume = {111}, number = {23}, pages = {235127}, abstract = {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 Fe3⁢Sn, 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 Fe3⁢Sn. 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.}, keywords = {A5}, pubstate = {published}, tppubtype = {article} } Close 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 Fe3⁢Sn, 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 Fe3⁢Sn. 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. Close https://link.aps.org/doi/10.1103/xmmr-mfv4 doi:10.1103/xmmr-mfv4 Close
Chmeruk, A.; Jones, D.; Balducci, R.; Ebad-Allah, J.; Beiuşeanu, F.; Schilberth, F.; Kassem, M. A.; Schade, U.; Veber, A.; Puskar, L.; Tabata, Y.; Waki, T.; Nakamura, H.; Kuntscher, C. A.; Östlin, A.; Chioncel, L. Suppression of magnetism in Co₃Sn₂S₂ under external pressure Unpublished (2025), arXiv:2511.08141. Abstract \| Links \| BibTeX \| Project(s): A1, A5 @unpublished{chmeruk_suppression_2025, title = {Suppression of magnetism in Co_{3}Sn_{2}S_{2} under external pressure}, author = {A. Chmeruk and D. Jones and R. Balducci and J. Ebad-Allah and F. Beiuşeanu and F. Schilberth and M. A. Kassem and U. Schade and A. Veber and L. Puskar and Y. Tabata and T. Waki and H. Nakamura and C. A. Kuntscher and A. Östlin and L. Chioncel}, url = {https://arxiv.org/abs/2511.08141}, doi = {10.48550/arXiv.2511.08141}, year = {2025}, date = {2025-11-01}, urldate = {2025-11-01}, abstract = {The ability to control the magnetic state provides a powerful means to tune the underlying band topology, enabling transitions between distinct electronic phases and the emergence of novel quantum phenomena. In this work, we address the evolution of ferromagnetic state upon applying external pressures up to 10.8~GPa using a combined experimental and theoretical study. The standard emph{ab initio} Density Functional Theory computation including ionic relaxations grossly overestimates the unit cell magnetization as a function of pressure. In our theoretical analysis we identify two possible mechanisms to remedy this shortcoming. Matching the experimental observations is achieved by a symmetry-preserving adjustment of the sulfur atoms position within the unit cell. Alternatively, we explore various combinations of the exchange and correlation parts of the effective potential which reproduce the experimental magnetization, the structural parameters and the measured optical conductivity spectra. Thus, the pressure-dependent behavior of magnetization demands a careful theoretical treatment and analysis of theoretical and experimental data. }, note = {arXiv:2511.08141}, keywords = {A1, A5}, pubstate = {published}, tppubtype = {unpublished} } Close The ability to control the magnetic state provides a powerful means to tune the underlying band topology, enabling transitions between distinct electronic phases and the emergence of novel quantum phenomena. In this work, we address the evolution of ferromagnetic state upon applying external pressures up to 10.8~GPa using a combined experimental and theoretical study. The standard emph{ab initio} Density Functional Theory computation including ionic relaxations grossly overestimates the unit cell magnetization as a function of pressure. In our theoretical analysis we identify two possible mechanisms to remedy this shortcoming. Matching the experimental observations is achieved by a symmetry-preserving adjustment of the sulfur atoms position within the unit cell. Alternatively, we explore various combinations of the exchange and correlation parts of the effective potential which reproduce the experimental magnetization, the structural parameters and the measured optical conductivity spectra. Thus, the pressure-dependent behavior of magnetization demands a careful theoretical treatment and analysis of theoretical and experimental data. Close https://arxiv.org/abs/2511.08141 doi:10.48550/arXiv.2511.08141 Close
2024
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). Abstract \| Links \| BibTeX \| Project(s): A1, A5 @article{prodan_anisotropic_2024, title = {Anisotropic charge transport in the easy-plane kagome ferromagnet Fe_{3}Sn}, author = {L. Prodan and A. Chmeruk and L. Chioncel and V. Tsurkan and I. Kézsmárki}, doi = {10.1103/PhysRevB.110.094407}, year = {2024}, date = {2024-09-05}, urldate = {2024-09-05}, journal = {Phys. Rev. B}, volume = {110}, number = {9}, pages = {094407}, abstract = {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 (𝜌𝑥⁢𝑥). 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 (𝜌𝐴𝑖⁢𝑗) shows large values over a wide temperature range and exhibits a significant anisotropy ratio (𝜌𝑥⁢𝑦/𝜌𝑧⁢𝑦), with 𝜌𝑥⁢𝑦 =8 µ⁢Ωcm and 𝜌𝑧⁢𝑦 =3.2 µ⁢Ωcm 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 Fe3⁢Sn. 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.}, keywords = {A1, A5}, pubstate = {published}, tppubtype = {article} } Close 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 (𝜌𝑥⁢𝑥). 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 (𝜌𝐴𝑖⁢𝑗) shows large values over a wide temperature range and exhibits a significant anisotropy ratio (𝜌𝑥⁢𝑦/𝜌𝑧⁢𝑦), with 𝜌𝑥⁢𝑦 =8 µ⁢Ωcm and 𝜌𝑧⁢𝑦 =3.2 µ⁢Ωcm 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 Fe3⁢Sn. 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. Close doi:10.1103/PhysRevB.110.094407 Close
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). Abstract \| Links \| BibTeX \| Project(s): A5 @article{jones_superconducting_2024, title = {Superconducting transition temperatures of pure vanadium and vanadium-titanium alloys in the presence of dynamical electronic correlations}, author = {D. Jones and A. Östlin and A. Weh and F. Beiuşeanu and U. Eckern and L. Vitos and L. Chioncel}, doi = {10.1103/PhysRevB.109.165107}, year = {2024}, date = {2024-04-01}, urldate = {2024-04-12}, journal = {Phys. Rev. B}, volume = {109}, number = {16}, pages = {165107}, abstract = {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%.}, keywords = {A5}, pubstate = {published}, tppubtype = {article} } Close 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%. Close doi:10.1103/PhysRevB.109.165107 Close
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 easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe₃Sn Journal Article Appl. Phys. Lett. 123, 021901 (2023). Abstract \| Links \| BibTeX \| Project(s): A4, A5 @article{prodan_large_2023, title = {Large ordered moment with strong easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe_{3}Sn}, author = {L. Prodan and D. M. Evans and S. M. Griffin and A. Oestlin and M. Altthaler and E. Lysne and I. G. Filippova and S. Shova and L. Chioncel and V. Tsurkan and I. Kézsmárki}, doi = {10.1063/5.0155295}, issn = {0003-6951}, year = {2023}, date = {2023-07-01}, urldate = {2023-07-01}, journal = {Appl. Phys. Lett.}, volume = {123}, number = {2}, pages = {021901}, abstract = {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).}, keywords = {A4, A5}, pubstate = {published}, tppubtype = {article} } Close 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). Close doi:10.1063/5.0155295 Close