2025
|
Schilberth, F.; Jiang, M. -C.; Mardelé, F. Le; Papp, L. B.; Mohelsky, I.; Kassem, M. A.; Tabata, Y.; Waki, T.; Nakamura, H.; Guo, G. -Y.; Orlita, M.; Arita, R.; Kézsmárki, I.; Bordács, S. Generation of a nodal line and Weyl points by magnetization reorientation in Co3Sn2S2 Journal Article npj Quantum Mater. 10, 67 (2025). @article{schilberth_generation_2025,
title = {Generation of a nodal line and Weyl points by magnetization reorientation in Co_{3}Sn_{2}S_{2}},
author = {F. Schilberth and M. -C. Jiang and F. Le Mardelé and L. B. Papp and I. Mohelsky and M. A. Kassem and Y. Tabata and T. Waki and H. Nakamura and G. -Y. Guo and M. Orlita and R. Arita and I. Kézsmárki and S. Bordács},
url = {https://doi.org/10.1038/s41535-025-00785-0},
doi = {10.1038/s41535-025-00785-0},
year = {2025},
date = {2025-07-01},
urldate = {2025-07-01},
journal = {npj Quantum Mater.},
volume = {10},
number = {1},
pages = {67},
abstract = {Topological magnets exhibit fascinating physics like topologically protected surface states and anomalous transport. Although these states and phenomena are expected to strongly depend on the magnetic order, their experimental manipulation has been scarcely studied. Here, we demonstrate the magnetic field control of the topological band structure in Co3Sn2S2 by magneto-optical spectroscopy. We resolve a magnetic field-induced redshift of the nodal loop resonance as the magnetization is rotated into the kagome plane. Our material-specific theory, capturing the observed field-induced spectral reconstruction, reveals the emergence of a gapless nodal loop for one of the in-plane magnetization directions. The calculations show that the additionally created Weyl points for in-plane fields marginally contribute to the optical response. These findings demonstrate that breaking underlying crystal symmetries with external fields provides an efficient way to manipulate topological band features. Moreover, our results highlight the potential of low-energy magneto-optical spectroscopy in probing variations of quantum geometry.},
keywords = {A1},
pubstate = {published},
tppubtype = {article}
}
Topological magnets exhibit fascinating physics like topologically protected surface states and anomalous transport. Although these states and phenomena are expected to strongly depend on the magnetic order, their experimental manipulation has been scarcely studied. Here, we demonstrate the magnetic field control of the topological band structure in Co3Sn2S2 by magneto-optical spectroscopy. We resolve a magnetic field-induced redshift of the nodal loop resonance as the magnetization is rotated into the kagome plane. Our material-specific theory, capturing the observed field-induced spectral reconstruction, reveals the emergence of a gapless nodal loop for one of the in-plane magnetization directions. The calculations show that the additionally created Weyl points for in-plane fields marginally contribute to the optical response. These findings demonstrate that breaking underlying crystal symmetries with external fields provides an efficient way to manipulate topological band features. Moreover, our results highlight the potential of low-energy magneto-optical spectroscopy in probing variations of quantum geometry. |  |
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. @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 = {2025-11-11},
urldate = {2025-11-11},
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}
}
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. | |
Schilberth, F.; DeFreitas, L.; Zhao, K.; LeMardelé, F.; Mohelsky, I.; Orlita, M.; Gegenwart, P.; Chen, H.; Kézsmárki, I.; Bordács, S. Large magnetoreflectance and optical anisotropy due to 4f flat bands in the frustrated kagome magnet HoAgGe Unpublished (2025), arXiv.2504.10274. @unpublished{schilberth_large_2025,
title = {Large magnetoreflectance and optical anisotropy due to 4f flat bands in the frustrated kagome magnet HoAgGe},
author = {F. Schilberth and L. DeFreitas and K. Zhao and F. LeMardelé and I. Mohelsky and M. Orlita and P. Gegenwart and H. Chen and I. Kézsmárki and S. Bordács},
url = {https://arxiv.org/abs/2504.10274},
doi = {10.48550/arXiv.2504.10274},
year = {2025},
date = {2025-04-14},
urldate = {2025-04-01},
abstract = {We report peculiar optical properties of the frustrated itinerant magnet HoAgGe, which exhibits multiple magnetically ordered states obeying the kagome spin-ice rule. The optical conductivity is surprisingly higher for light polarization perpendicular to the kagome plane, both for the free carrier response and the interband transitions. The latter ones have strong contributions from Ho 4f flat bands located near the Fermi level, as revealed by our textbackslashtextitab initio calculations, explaining the unusual anisotropy of the optical properties and the pronounced temperature dependence of the interband transitions for out–of–plane light polarization. The key role of Ho 4f states is further supported by the large variation of the reflectivity upon the metamagnetic transitions, that follows the field dependence of the magnetization, in contrast to that of the dc magnetotransport data. Such heavy-electron bands near the Fermi level offer an efficient way to control transport and optical properties.},
note = {arXiv.2504.10274},
keywords = {A1, B3},
pubstate = {published},
tppubtype = {unpublished}
}
We report peculiar optical properties of the frustrated itinerant magnet HoAgGe, which exhibits multiple magnetically ordered states obeying the kagome spin-ice rule. The optical conductivity is surprisingly higher for light polarization perpendicular to the kagome plane, both for the free carrier response and the interband transitions. The latter ones have strong contributions from Ho 4f flat bands located near the Fermi level, as revealed by our textbackslashtextitab initio calculations, explaining the unusual anisotropy of the optical properties and the pronounced temperature dependence of the interband transitions for out–of–plane light polarization. The key role of Ho 4f states is further supported by the large variation of the reflectivity upon the metamagnetic transitions, that follows the field dependence of the magnetization, in contrast to that of the dc magnetotransport data. Such heavy-electron bands near the Fermi level offer an efficient way to control transport and optical properties. |  |
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). @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 (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.},
keywords = {A1, A5},
pubstate = {published},
tppubtype = {article}
}
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. | |
Vasin, K. V.; Strinić, A.; Schilberth, F.; Reschke, S.; Prodan, L.; Tsurkan, V.; Nurmukhametov, A. R.; Eremin, M. V.; Kézsmárki, I.; Deisenhofer, J. Optical magnetoelectric effect in the polar honeycomb antiferromagnet Fe2Mo3O8 Journal Article Phys. Rev. B 110, 054401 (2024). @article{vasin_optical_2024,
title = {Optical magnetoelectric effect in the polar honeycomb antiferromagnet Fe_{2}Mo_{3}O_{8}},
author = {K. V. Vasin and A. Strinić and F. Schilberth and S. Reschke and L. Prodan and V. Tsurkan and A. R. Nurmukhametov and M. V. Eremin and I. Kézsmárki and J. Deisenhofer},
doi = {10.1103/PhysRevB.110.054401},
year = {2024},
date = {2024-08-01},
urldate = {2024-08-01},
journal = {Phys. Rev. B},
volume = {110},
number = {5},
pages = {054401},
abstract = {The lack of both time-reversal and spatial inversion symmetry in polar magnets is a prerequisite for the occurrence of optical magnetoelectric effects such as nonreciprocal directional dichroism, i.e., a difference in refractive index and absorption for two counter-propagating electromagnetic waves, which has the potential for the realization of optical diodes. In particular, antiferromagnetic materials with magnetic excitations in the THz range such as Fe2Mo3O8 are promising candidates for next-generation spintronic applications. In a combined experimental and theoretical effort we investigated the THz excitations of the polar honeycomb antiferromagnet Fe2Mo3O8 in external magnetic fields and their nonreciprocal directional dichroism, together with the temperature dependence of the electronic transitions in the mid- and near-infrared frequency range. Using an advanced single-ion approach for the Fe ions, we are able to describe optical excitations from the THz to the near-infrared frequency range quantitatively and model the observed nonreciprocal directional dichroism in the THz regime successfully.},
keywords = {A1, C4},
pubstate = {published},
tppubtype = {article}
}
The lack of both time-reversal and spatial inversion symmetry in polar magnets is a prerequisite for the occurrence of optical magnetoelectric effects such as nonreciprocal directional dichroism, i.e., a difference in refractive index and absorption for two counter-propagating electromagnetic waves, which has the potential for the realization of optical diodes. In particular, antiferromagnetic materials with magnetic excitations in the THz range such as Fe2Mo3O8 are promising candidates for next-generation spintronic applications. In a combined experimental and theoretical effort we investigated the THz excitations of the polar honeycomb antiferromagnet Fe2Mo3O8 in external magnetic fields and their nonreciprocal directional dichroism, together with the temperature dependence of the electronic transitions in the mid- and near-infrared frequency range. Using an advanced single-ion approach for the Fe ions, we are able to describe optical excitations from the THz to the near-infrared frequency range quantitatively and model the observed nonreciprocal directional dichroism in the THz regime successfully. |  |
Magnaterra, M.; Attig, J.; Peterlini, L.; Hermanns, M.; Upton, M. H.; Kim, Jungho; Prodan, L.; Tsurkan, V.; Kézsmárki, I.; Loosdrecht, P. H. M.; Grüninger, M. Quasimolecular Jtet = 3/2 Moments in the Cluster Mott Insulator GaTa4Se8 Journal Article Phys. Rev. Lett. 133, 046501 (2024). @article{magnaterra_quasimolecular_2024,
title = {Quasimolecular J_{tet} = 3/2 Moments in the Cluster Mott Insulator GaTa_{4}Se_{8}},
author = {M. Magnaterra and J. Attig and L. Peterlini and M. Hermanns and M. H. Upton and Jungho Kim and L. Prodan and V. Tsurkan and I. Kézsmárki and P. H. M. Loosdrecht and M. Grüninger},
doi = {10.1103/PhysRevLett.133.046501},
year = {2024},
date = {2024-07-22},
urldate = {2024-07-22},
journal = {Phys. Rev. Lett.},
volume = {133},
number = {4},
pages = {046501},
keywords = {A1},
pubstate = {published},
tppubtype = {article}
}
| |
Kumar, H.; Köpf, M.; Telang, P.; Bura, N.; Jesche, A.; Gegenwart, P.; Kuntscher, C. A. Optical conductivity of the metallic pyrochlore iridate Pr2Ir2O7: Influence of spin-orbit coupling and electronic correlations on the electronic structure Journal Article Phys. Rev. B 110, 035140 (2024). @article{kumar_optical_2024,
title = {Optical conductivity of the metallic pyrochlore iridate Pr_{2}Ir_{2}O_{7}: Influence of spin-orbit coupling and electronic correlations on the electronic structure},
author = {H. Kumar and M. Köpf and P. Telang and N. Bura and A. Jesche and P. Gegenwart and C. A. Kuntscher},
url = {https://link.aps.org/doi/10.1103/PhysRevB.110.035140},
doi = {10.1103/PhysRevB.110.035140},
year = {2024},
date = {2024-07-15},
urldate = {2024-07-01},
journal = {Phys. Rev. B},
volume = {110},
number = {3},
pages = {035140},
abstract = {The synergy of strong spin-orbit coupling and electron-electron interactions gives rise to unconventional topological states, such as topological Mott insulator, Weyl semimetal, and quantum spin liquid. In this study, we have grown single crystals of the pyrochlore iridate Pr2Ir2O7 and explored its magnetic, lattice dynamical, and electronic properties. While Raman spectroscopy data reveal six phonon modes confirming the cubic Fd‾3m crystal symmetry, dc magnetic susceptibility data show no anomalies and hence indicate the absence of magnetic phase transitions down to 2 K. Both temperature-dependent electric transport and optical conductivity data reveal the metallic character of Pr2Ir2O7. The optical conductivity spectrum contains a midinfrared absorption band, which becomes more pronounced with decreasing temperature due to spectral weight transfer from high to low energies. The presence of the midinfrared band hints at the importance of correlation physics. The optical response furthermore suggests that Pr2Ir2O7 is close to the Weyl semimetal phase.},
keywords = {A1, B5},
pubstate = {published},
tppubtype = {article}
}
The synergy of strong spin-orbit coupling and electron-electron interactions gives rise to unconventional topological states, such as topological Mott insulator, Weyl semimetal, and quantum spin liquid. In this study, we have grown single crystals of the pyrochlore iridate Pr2Ir2O7 and explored its magnetic, lattice dynamical, and electronic properties. While Raman spectroscopy data reveal six phonon modes confirming the cubic Fd‾3m crystal symmetry, dc magnetic susceptibility data show no anomalies and hence indicate the absence of magnetic phase transitions down to 2 K. Both temperature-dependent electric transport and optical conductivity data reveal the metallic character of Pr2Ir2O7. The optical conductivity spectrum contains a midinfrared absorption band, which becomes more pronounced with decreasing temperature due to spectral weight transfer from high to low energies. The presence of the midinfrared band hints at the importance of correlation physics. The optical response furthermore suggests that Pr2Ir2O7 is close to the Weyl semimetal phase. | |
Kunze, J.; Köpf, M.; Cao, W.; Qi, Y.; Kuntscher, C. A. Optical signatures of type-II Weyl fermions in the noncentrosymmetric semimetals RAlSi (R = La, Ce, Pr, Nd, Sm) Journal Article Phys. Rev. B 109, 195130 (2024). @article{kunze_optical_2024,
title = {Optical signatures of type-II Weyl fermions in the noncentrosymmetric semimetals RAlSi (R = La, Ce, Pr, Nd, Sm)},
author = {J. Kunze and M. Köpf and W. Cao and Y. Qi and C. A. Kuntscher},
url = {https://link.aps.org/doi/10.1103/PhysRevB.109.195130},
doi = {10.1103/PhysRevB.109.195130},
year = {2024},
date = {2024-05-09},
urldate = {2024-05-09},
journal = {Phys. Rev. B},
volume = {109},
number = {19},
pages = {195130},
abstract = {Weyl semimetals with magnetic ordering provide a promising platform for the investigation of rare topological effects such as the anomalous Hall effect, resulting from the interplay of nontrivial bands with various spin configurations. The materials RAlSi, where R represents a rare-earth element, are prominent representatives of Weyl semimetals, where the Weyl states are induced by space inversion symmetry breaking, and in addition, for several rare-earth elements R, enhanced by time-reversal symmetry breaking through the formation of a magnetic order at low temperature. We report optical signatures of Weyl fermions in the magnetic compounds CeAlSi, PrAlSi, NdAlSi, and SmAlSi as well as the nonmagnetic family member LaAlSi by broad-frequency infrared spectroscopy at room temperature, i.e., in the paramagnetic phase. A similar profile of the optical conductivity spectrum and a metallic character are observed for all compounds, with LaAlSi showing the strongest free charge-carrier contribution. Furthermore, the linear-in-frequency behavior of the optical conductivity of all investigated compounds indicates the presence of Weyl nodes in close proximity to the Fermi energy, resulting from inversion symmetry breaking in noncentrosymmetric structures. According to the characteristics of these linear slopes, the RAlSi compounds are expected to host mainly type-II Weyl states with overtilted Weyl cones. The results are compared to the optical response of the closely related RAlGe materials, which are considered as potential hybridization-driven Weyl-Kondo systems.},
keywords = {A1},
pubstate = {published},
tppubtype = {article}
}
Weyl semimetals with magnetic ordering provide a promising platform for the investigation of rare topological effects such as the anomalous Hall effect, resulting from the interplay of nontrivial bands with various spin configurations. The materials RAlSi, where R represents a rare-earth element, are prominent representatives of Weyl semimetals, where the Weyl states are induced by space inversion symmetry breaking, and in addition, for several rare-earth elements R, enhanced by time-reversal symmetry breaking through the formation of a magnetic order at low temperature. We report optical signatures of Weyl fermions in the magnetic compounds CeAlSi, PrAlSi, NdAlSi, and SmAlSi as well as the nonmagnetic family member LaAlSi by broad-frequency infrared spectroscopy at room temperature, i.e., in the paramagnetic phase. A similar profile of the optical conductivity spectrum and a metallic character are observed for all compounds, with LaAlSi showing the strongest free charge-carrier contribution. Furthermore, the linear-in-frequency behavior of the optical conductivity of all investigated compounds indicates the presence of Weyl nodes in close proximity to the Fermi energy, resulting from inversion symmetry breaking in noncentrosymmetric structures. According to the characteristics of these linear slopes, the RAlSi compounds are expected to host mainly type-II Weyl states with overtilted Weyl cones. The results are compared to the optical response of the closely related RAlGe materials, which are considered as potential hybridization-driven Weyl-Kondo systems. | |
Ebad-Allah, J.; Jiang, M. -C.; Borkenhagen, R.; Meggle, F.; Prodan, L.; Tsurkan, V.; Schilberth, F.; Guo, G. -Y.; Arita, R.; Kézsmárki, I.; Kuntscher, C. A. Optical anisotropy of the kagome magnet FeSn: Dominant role of excitations between kagome and Sn layers Journal Article Phys. Rev. B 109, L201106 (2024). @article{ebad-allah_optical_2024,
title = {Optical anisotropy of the kagome magnet FeSn: Dominant role of excitations between kagome and Sn layers},
author = {J. Ebad-Allah and M. -C. Jiang and R. Borkenhagen and F. Meggle and L. Prodan and V. Tsurkan and F. Schilberth and G. -Y. Guo and R. Arita and I. Kézsmárki and C. A. Kuntscher},
doi = {10.1103/PhysRevB.109.L201106},
year = {2024},
date = {2024-05-07},
urldate = {2024-05-01},
journal = {Phys. Rev. B},
volume = {109},
number = {20},
pages = {L201106},
abstract = {Antiferromagnetic FeSn is considered to be a close realization of the ideal two-dimensional (2D) kagome lattice, hosting Dirac cones, van Hove singularities, and flat bands, as it comprises Fe3Sn kagome layers well separated by Sn buffer layers. We observe a pronounced optical anisotropy, with the low-energy optical conductivity being surprisingly higher perpendicular to the kagome planes than along the layers. This finding contradicts the prevalent picture of dominantly 2D electronic structure for FeSn. Our material-specific theory reproduces the measured conductivity spectra remarkably well. A site-specific decomposition of the optical response to individual excitation channels shows that the optical conductivity for polarizations both parallel and perpendicular to the kagome plane is dominated by interlayer transitions between kagome layers and adjacent Sn-based layers. Moreover, the matrix elements corresponding to these transitions are highly anisotropic, leading to larger out-of-plane conductivity. Our results evidence the crucial role of interstitial layers in charge dynamics even in seemingly 2D systems.},
keywords = {A1},
pubstate = {published},
tppubtype = {article}
}
Antiferromagnetic FeSn is considered to be a close realization of the ideal two-dimensional (2D) kagome lattice, hosting Dirac cones, van Hove singularities, and flat bands, as it comprises Fe3Sn kagome layers well separated by Sn buffer layers. We observe a pronounced optical anisotropy, with the low-energy optical conductivity being surprisingly higher perpendicular to the kagome planes than along the layers. This finding contradicts the prevalent picture of dominantly 2D electronic structure for FeSn. Our material-specific theory reproduces the measured conductivity spectra remarkably well. A site-specific decomposition of the optical response to individual excitation channels shows that the optical conductivity for polarizations both parallel and perpendicular to the kagome plane is dominated by interlayer transitions between kagome layers and adjacent Sn-based layers. Moreover, the matrix elements corresponding to these transitions are highly anisotropic, leading to larger out-of-plane conductivity. Our results evidence the crucial role of interstitial layers in charge dynamics even in seemingly 2D systems. | |
2023
|
Ghara, S.; Barts, E.; Vasin, K. V.; Kamenskyi, D.; Prodan, L.; Tsurkan, V.; Kézsmárki, I.; Mostovoy, M.; Deisenhofer, J. Magnetization reversal through an antiferromagnetic state Journal Article Nat. Commun. 14, 5174 (2023). @article{ghara_magnetization_2023,
title = {Magnetization reversal through an antiferromagnetic state},
author = {S. Ghara and E. Barts and K. V. Vasin and D. Kamenskyi and L. Prodan and V. Tsurkan and I. Kézsmárki and M. Mostovoy and J. Deisenhofer},
doi = {10.1038/s41467-023-40722-y},
year = {2023},
date = {2023-08-01},
urldate = {2023-08-01},
journal = {Nat. Commun.},
volume = {14},
number = {1},
pages = {5174},
abstract = {Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe2Mo3O8. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders.},
keywords = {A1, C4},
pubstate = {published},
tppubtype = {article}
}
Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe2Mo3O8. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders. |  |
Schilberth, F.; Jiang, M. -C.; Minami, S.; Kassem, M. A.; Mayr, F.; Koretsune, T.; Tabata, Y.; Waki, T.; Nakamura, H.; Guo, G. -Y.; Arita, R.; Kézsmárki, I.; Bordacs, S. Nodal-line resonance generating the giant anomalous Hall effect of Co3Sn2S2 Journal Article Phys. Rev. B 107, 214441 (2023). @article{schilberth_nodal-line_2023,
title = {Nodal-line resonance generating the giant anomalous Hall effect of Co_{3}Sn_{2}S_{2}},
author = {F. Schilberth and M. -C. Jiang and S. Minami and M. A. Kassem and F. Mayr and T. Koretsune and Y. Tabata and T. Waki and H. Nakamura and G. -Y. Guo and R. Arita and I. Kézsmárki and S. Bordacs},
doi = {10.1103/PhysRevB.107.214441},
issn = {2469-9950},
year = {2023},
date = {2023-06-01},
urldate = {2023-06-01},
journal = {Phys. Rev. B},
volume = {107},
number = {21},
pages = {214441},
abstract = {Giant anomalous Hall effect (AHE) and magneto-optical activity can emerge in magnets with topologically nontrivial degeneracies. However, identifying the specific band-structure features such as Weyl points, nodal lines, or planes which generate the anomalous response is a challenging issue. Since the low-energy interband transitions can govern the static AHE, we addressed this question in the prototypical magnetic Weyl semimetal Co3Sn2S2 also hosting nodal lines by broadband polarized reflectivity and magneto-optical Kerr effect spectroscopy with a focus on the far-infrared range. In the linear dichroism spectrum we observe a strong resonance at 40 meV, which also appears in the optical Hall conductivity and primarily determines the static AHE, and thus confirms its intrinsic origin. Our material-specific theory reproduces the experimental data remarkably well and shows that strongly tilted nodal-line segments around the Fermi energy generate the resonance. While the Weyl points only give vanishing contributions, these segments of the nodal lines gapped by the spin-orbit coupling dominate the low-energy optical response and generate the giant AHE.},
keywords = {A1},
pubstate = {published},
tppubtype = {article}
}
Giant anomalous Hall effect (AHE) and magneto-optical activity can emerge in magnets with topologically nontrivial degeneracies. However, identifying the specific band-structure features such as Weyl points, nodal lines, or planes which generate the anomalous response is a challenging issue. Since the low-energy interband transitions can govern the static AHE, we addressed this question in the prototypical magnetic Weyl semimetal Co3Sn2S2 also hosting nodal lines by broadband polarized reflectivity and magneto-optical Kerr effect spectroscopy with a focus on the far-infrared range. In the linear dichroism spectrum we observe a strong resonance at 40 meV, which also appears in the optical Hall conductivity and primarily determines the static AHE, and thus confirms its intrinsic origin. Our material-specific theory reproduces the experimental data remarkably well and shows that strongly tilted nodal-line segments around the Fermi energy generate the resonance. While the Weyl points only give vanishing contributions, these segments of the nodal lines gapped by the spin-orbit coupling dominate the low-energy optical response and generate the giant AHE. |  |
