2025
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Yamada, R.; Birch, M. T.; Baral, P. R.; Okumura, S.; Nakano, R.; Gao, S.; Ezawa, M.; Nomoto, T.; Masell, J.; Ishihara, Y.; Kolincio, K. K.; Belopolski, I.; Sagayama, H.; Nakao, H.; Ohishi, K.; Ohhara, T.; Kiyanagi, R.; Nakajima, T.; Tokura, Y.; Arima, T.; Motome, Y.; Hirschmann, M. M.; Hirschberger, M. A metallic p-wave magnet with commensurate spin helix Journal Article Nature 646, 837 (2025). @article{yamada_metallic_2025,
title = {A metallic p-wave magnet with commensurate spin helix},
author = {R. Yamada and M. T. Birch and P. R. Baral and S. Okumura and R. Nakano and S. Gao and M. Ezawa and T. Nomoto and J. Masell and Y. Ishihara and K. K. Kolincio and I. Belopolski and H. Sagayama and H. Nakao and K. Ohishi and T. Ohhara and R. Kiyanagi and T. Nakajima and Y. Tokura and T. Arima and Y. Motome and M. M. Hirschmann and M. Hirschberger},
url = {https://doi.org/10.1038/s41586-025-09633-4},
doi = {10.1038/s41586-025-09633-4},
year = {2025},
date = {2025-10-22},
urldate = {2025-10-01},
journal = {Nature},
volume = {646},
number = {8086},
pages = {837},
abstract = {Antiferromagnetic states with a spin-split electronic structure give rise to spintronic, magnonic and electronic phenomena despite (near-)zero net magnetization [1–7]. The simplest odd-parity spin splitting—p wave—was originally proposed to emerge from a collective instability in interacting electron systems [8–12]. Recent theory has identified a distinct route to realize p-wave spin-split electronic bands without strong correlations [13,14], termed p-wave magnetism. Here we demonstrate an experimental realization of a metallic p-wave magnet. The odd-parity spin splitting of delocalized conduction electrons arises from their coupling to an antiferromagnetic texture of localized magnetic moments: a coplanar spin helix whose magnetic period is an even multiple of the chemical unit cell, as revealed by X-ray scattering experiments. This texture breaks space-inversion symmetry but approximately preserves time-reversal symmetry up to a half-unit-cell translation—thereby fulfilling the symmetry conditions for p-wave magnetism. Consistent with theoretical predictions, our p-wave magnet shows a characteristic anisotropy in the electronic conductivity [13–15]. Relativistic spin–orbit coupling and a tiny spontaneous net magnetization further break time-reversal symmetry, resulting in a giant anomalous Hall effect (Hall conductivity >600 S cm−1, Hall angle >3%), for an antiferromagnet. Our model calculations show that the spin-nodal planes found in the electronic structure of p-wave magnets are readily gapped by a small perturbation to induce the anomalous Hall effect. We establish metallic p-wave magnets as an ideal platform to explore the functionality of spin-split electronic states in magnets, superconductors, and in spintronic devices.},
keywords = {B5},
pubstate = {published},
tppubtype = {article}
}
Antiferromagnetic states with a spin-split electronic structure give rise to spintronic, magnonic and electronic phenomena despite (near-)zero net magnetization [1–7]. The simplest odd-parity spin splitting—p wave—was originally proposed to emerge from a collective instability in interacting electron systems [8–12]. Recent theory has identified a distinct route to realize p-wave spin-split electronic bands without strong correlations [13,14], termed p-wave magnetism. Here we demonstrate an experimental realization of a metallic p-wave magnet. The odd-parity spin splitting of delocalized conduction electrons arises from their coupling to an antiferromagnetic texture of localized magnetic moments: a coplanar spin helix whose magnetic period is an even multiple of the chemical unit cell, as revealed by X-ray scattering experiments. This texture breaks space-inversion symmetry but approximately preserves time-reversal symmetry up to a half-unit-cell translation—thereby fulfilling the symmetry conditions for p-wave magnetism. Consistent with theoretical predictions, our p-wave magnet shows a characteristic anisotropy in the electronic conductivity [13–15]. Relativistic spin–orbit coupling and a tiny spontaneous net magnetization further break time-reversal symmetry, resulting in a giant anomalous Hall effect (Hall conductivity >600 S cm−1, Hall angle >3%), for an antiferromagnet. Our model calculations show that the spin-nodal planes found in the electronic structure of p-wave magnets are readily gapped by a small perturbation to induce the anomalous Hall effect. We establish metallic p-wave magnets as an ideal platform to explore the functionality of spin-split electronic states in magnets, superconductors, and in spintronic devices. |  |
Tang, N.; Glamsch, S.; Aqeel, A.; Scheuchenpflug, L.; Schulze, M.; Liebald, C.; Rytz, D.; Guguschev, C.; Albrecht, M.; Gegenwart, P. Observation via spin Seebeck effect of macroscopic magnetic transport from emergent magnetic monopoles Unpublished (2025), arXiv:2509.18422. @unpublished{tang_observation_2025,
title = {Observation via spin Seebeck effect of macroscopic magnetic transport from emergent magnetic monopoles},
author = {N. Tang and S. Glamsch and A. Aqeel and L. Scheuchenpflug and M. Schulze and C. Liebald and D. Rytz and C. Guguschev and M. Albrecht and P. Gegenwart},
url = {https://arxiv.org/abs/2509.18422},
doi = {10.48550/arXiv.2509.18422},
year = {2025},
date = {2025-09-22},
urldate = {2025-09-22},
abstract = {Magnetic monopoles, elusive in high-energy physics, have been realised as emergent quasiparticles in solid-state systems, where their unique properties hold promise for novel spintronic applications. Magnetic monopoles have been invoked in diverse platforms, including skyrmion lattices, chiral magnets, soft ferromagnets, aritifical nanomagnets. Yet, a demonstration of their role in magnetic transport has remained elusive. Here, we report such an observation via the spin Seebeck effect in the bulk insulating pyrochlore oxide, spin ice Dy2Ti2O7. By applying a thermal gradient perpendicular to a [111]-oriented magnetic field, we detect a transverse spin Seebeck voltage marked by a dominant peak at the onset of monopole proliferation, accompanied by a secondary feature and frequency-dependent behavior. Our findings establish a direct link between monopole dynamics and magnetic transport in an insulating medium, establishing a new pathway for probing fractionalized excitations and advancing towards novel spintronic applications.},
note = {arXiv:2509.18422},
keywords = {A2, B5},
pubstate = {published},
tppubtype = {unpublished}
}
Magnetic monopoles, elusive in high-energy physics, have been realised as emergent quasiparticles in solid-state systems, where their unique properties hold promise for novel spintronic applications. Magnetic monopoles have been invoked in diverse platforms, including skyrmion lattices, chiral magnets, soft ferromagnets, aritifical nanomagnets. Yet, a demonstration of their role in magnetic transport has remained elusive. Here, we report such an observation via the spin Seebeck effect in the bulk insulating pyrochlore oxide, spin ice Dy2Ti2O7. By applying a thermal gradient perpendicular to a [111]-oriented magnetic field, we detect a transverse spin Seebeck voltage marked by a dominant peak at the onset of monopole proliferation, accompanied by a secondary feature and frequency-dependent behavior. Our findings establish a direct link between monopole dynamics and magnetic transport in an insulating medium, establishing a new pathway for probing fractionalized excitations and advancing towards novel spintronic applications. |  |
Scheuchenpflug, L.; Esser, S.; Gruhl, R.; Hirschberger, M.; Gegenwart, P. Current-linear emergent induction of pinned skyrmion textures in an oxide bilayer Unpublished (2025), arXiv:2503.10600. @unpublished{scheuchenpflug_current-linear_2025,
title = {Current-linear emergent induction of pinned skyrmion textures in an oxide bilayer},
author = {L. Scheuchenpflug and S. Esser and R. Gruhl and M. Hirschberger and P. Gegenwart},
url = {https://arxiv.org/abs/2503.10600},
doi = {10.48550/arXiv.2503.10600},
year = {2025},
date = {2025-03-13},
urldate = {2025-03-13},
abstract = {Emergent electromagnetic induction (EEMI) induced through current-driven spin dynamics was recently predicted and subsequently observed in helical spin magnets, opening a new direction in spintronics and paving the way towards further miniaturization of electronic circuit elements. In contrast to conventional inductors consisting of coil-like structures whose inductance shows a linear dependence on the cross-section , emergent inductors exhibit an inverse (textasciitildeAˆ-1) proportionality, favorable for the miniaturization of electrical devices. However, the expected current-linear response of the EEMI voltage has not been demonstrated. Magnetic skyrmions hold promise as a simple platform to study the conceptual foundations of EEMI from current-driven spin dynamics. We fabricated devices of thin film bilayers of ferromagnetic SrRuO3 and paramagnetic SrIrO3, which are known to host interfacial Néel skyrmions detected by the appearance of a topological Hall-effect (THE). A large, positive and current-linear inductive response is found to accompany the THE. In our experiment, the current-induced dynamics of pinned magnetic skyrmions creates a voltage both parallel and perpendicular to the applied electric current flow, corresponding to longitudinal and transverse induction, respectively. This is the first report of transverse EEMI, indicating an angle of 80° between skyrmion motion and the applied current. Our observation of current-linear longitudinal and transverse EEMI is a hallmark of pinned dynamics of magnetic skyrmion textures in oxide heterostructures.},
note = {arXiv:2503.10600},
keywords = {B5},
pubstate = {published},
tppubtype = {unpublished}
}
Emergent electromagnetic induction (EEMI) induced through current-driven spin dynamics was recently predicted and subsequently observed in helical spin magnets, opening a new direction in spintronics and paving the way towards further miniaturization of electronic circuit elements. In contrast to conventional inductors consisting of coil-like structures whose inductance shows a linear dependence on the cross-section , emergent inductors exhibit an inverse (textasciitildeAˆ-1) proportionality, favorable for the miniaturization of electrical devices. However, the expected current-linear response of the EEMI voltage has not been demonstrated. Magnetic skyrmions hold promise as a simple platform to study the conceptual foundations of EEMI from current-driven spin dynamics. We fabricated devices of thin film bilayers of ferromagnetic SrRuO3 and paramagnetic SrIrO3, which are known to host interfacial Néel skyrmions detected by the appearance of a topological Hall-effect (THE). A large, positive and current-linear inductive response is found to accompany the THE. In our experiment, the current-induced dynamics of pinned magnetic skyrmions creates a voltage both parallel and perpendicular to the applied electric current flow, corresponding to longitudinal and transverse induction, respectively. This is the first report of transverse EEMI, indicating an angle of 80° between skyrmion motion and the applied current. Our observation of current-linear longitudinal and transverse EEMI is a hallmark of pinned dynamics of magnetic skyrmion textures in oxide heterostructures. | |
2024
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Tang, N.; Gen, M.; Rotter, M.; Man, H.; Matsuhira, K.; Matsuo, A.; Kindo, K.; Ikeda, A.; Matsuda, Y.; Gegenwart, P.; Nakatsuji, S.; Kohama, Y. Crystal field magnetostriction of spin ice under ultrahigh magnetic fields Journal Article Phys. Rev. B 110, 214414 (2024). @article{tang_crystal_2024,
title = {Crystal field magnetostriction of spin ice under ultrahigh magnetic fields},
author = {N. Tang and M. Gen and M. Rotter and H. Man and K. Matsuhira and A. Matsuo and K. Kindo and A. Ikeda and Y. Matsuda and P. Gegenwart and S. Nakatsuji and Y. Kohama},
url = {https://link.aps.org/doi/10.1103/PhysRevB.110.214414},
doi = {10.1103/PhysRevB.110.214414},
year = {2024},
date = {2024-12-09},
urldate = {2024-12-01},
journal = {Phys. Rev. B},
volume = {110},
number = {21},
pages = {214414},
abstract = {We present a comprehensive study of the magnetoelastic properties of the Ising pyrochlore oxide Ho2Ti2O7, known as spin ice, by means of high-field magnetostriction measurements and numerical calculations. When a magnetic field is applied along the crystallographic ⟨111⟩ axis, the longitudinal magnetostriction exhibits a broad maximum in the low-field regime around 30 T, followed by a dramatic lattice contraction due to crystal-field (CF) level crossing at 𝐵cf∼65 T. The transverse magnetostriction exhibits a contrasting behavior, highlighting the anisotropic nature of the CF striction. By applying a magnetic field at varying sweep rates, we identify distinct timescales of spin dynamics that are relevant to monopole formation and annihilation, as well as CF-phonon dynamics. Our mean-field calculations, based on a point-charge model, successfully reproduce the overall magnetostriction behavior, revealing the competition between the exchange striction and CF striction. A signature of the CF level crossing is also observed through adiabatic magnetocaloric-effect measurements, consistent with our magnetostriction data.},
keywords = {B3, B5},
pubstate = {published},
tppubtype = {article}
}
We present a comprehensive study of the magnetoelastic properties of the Ising pyrochlore oxide Ho2Ti2O7, known as spin ice, by means of high-field magnetostriction measurements and numerical calculations. When a magnetic field is applied along the crystallographic ⟨111⟩ axis, the longitudinal magnetostriction exhibits a broad maximum in the low-field regime around 30 T, followed by a dramatic lattice contraction due to crystal-field (CF) level crossing at 𝐵cf∼65 T. The transverse magnetostriction exhibits a contrasting behavior, highlighting the anisotropic nature of the CF striction. By applying a magnetic field at varying sweep rates, we identify distinct timescales of spin dynamics that are relevant to monopole formation and annihilation, as well as CF-phonon dynamics. Our mean-field calculations, based on a point-charge model, successfully reproduce the overall magnetostriction behavior, revealing the competition between the exchange striction and CF striction. A signature of the CF level crossing is also observed through adiabatic magnetocaloric-effect measurements, consistent with our magnetostriction data. | |
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. | |
Hirschberger, M.; Szigeti, B. G.; Hemmida, M.; Hirschmann, M. M.; Esser, S.; Ohsumi, H.; Tanaka, Y.; Spitz, L.; Gao, S.; Kolincio, K. K.; Sagayama, H.; Nakao, H.; Yamasaki, Y.; Forró, L.; von Nidda, H. -A. Krug; Kézsmárki, I.; Arima, T.; Tokura, Y. Lattice-commensurate skyrmion texture in a centrosymmetric breathing kagome magnet Journal Article npj Quantum Mater. 9, 45 (2024). @article{hirschberger_lattice-commensurate_2024,
title = {Lattice-commensurate skyrmion texture in a centrosymmetric breathing kagome magnet},
author = {M. Hirschberger and B. G. Szigeti and M. Hemmida and M. M. Hirschmann and S. Esser and H. Ohsumi and Y. Tanaka and L. Spitz and S. Gao and K. K. Kolincio and H. Sagayama and H. Nakao and Y. Yamasaki and L. Forró and H. -A. Krug von Nidda and I. Kézsmárki and T. Arima and Y. Tokura},
doi = {10.1038/s41535-024-00654-2},
year = {2024},
date = {2024-05-23},
urldate = {2024-05-01},
journal = {npj Quantum Mater.},
volume = {9},
pages = {45},
abstract = {Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. We reveal the commensurate locking of a SkL to the atomic lattice in Gd3Ru4Al12 via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a site of the atomic lattice. Under these conditions, a commensurate SkL, locked to the crystal lattice, is stable at finite temperatures – but gives way to a competing incommensurate ground state upon cooling. We discuss the role of Umklapp-terms in the Hamiltonian for the formation of this lattice-locked state, its magnetic space group, and the role of slight discommensurations, or (line) defects in the magnetic texture. We also contrast our findings with the case of SkLs in noncentrosymmetric material platforms.},
keywords = {B4, B5},
pubstate = {published},
tppubtype = {article}
}
Skyrmion lattices (SkL) in centrosymmetric materials typically have a magnetic period on the nanometer-scale, so that the coupling between magnetic superstructures and the underlying crystal lattice cannot be neglected. We reveal the commensurate locking of a SkL to the atomic lattice in Gd3Ru4Al12 via high-resolution resonant elastic x-ray scattering (REXS). Weak easy-plane magnetic anisotropy, demonstrated here by a combination of ferromagnetic resonance and REXS, penalizes placing a skyrmion core on a site of the atomic lattice. Under these conditions, a commensurate SkL, locked to the crystal lattice, is stable at finite temperatures – but gives way to a competing incommensurate ground state upon cooling. We discuss the role of Umklapp-terms in the Hamiltonian for the formation of this lattice-locked state, its magnetic space group, and the role of slight discommensurations, or (line) defects in the magnetic texture. We also contrast our findings with the case of SkLs in noncentrosymmetric material platforms. | |
Reinhoffer, C.; Esser, S.; Esser, S.; Mashkovich, E.; Germanskiy, S.; Gegenwart, P.; Anders, F.; Loosdrecht, P. H. M.; Wang, Z. Strong Terahertz Third-Harmonic Generation by Kinetic Heavy Quasiparticles in CaRuO3 Journal Article Phys. Rev. Lett. 132, 196501 (2024). @article{reinhoffer_strong_2024,
title = {Strong Terahertz Third-Harmonic Generation by Kinetic Heavy Quasiparticles in CaRuO_{3}},
author = {C. Reinhoffer and S. Esser and S. Esser and E. Mashkovich and S. Germanskiy and P. Gegenwart and F. Anders and P. H. M. Loosdrecht and Z. Wang},
url = {https://link.aps.org/doi/10.1103/PhysRevLett.132.196501},
doi = {10.1103/PhysRevLett.132.196501},
year = {2024},
date = {2024-05-08},
urldate = {2024-05-08},
journal = {Phys. Rev. Lett.},
volume = {132},
number = {19},
pages = {196501},
abstract = {We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO_{3}, as a function of temperature, frequency, and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle band emerges by strong correlations associated with the Hund’s coupling. Phenomenologically, by taking an experimentally observed frequency-dependent scattering rate, the deviation of the field driven kinetics from the Drude behavior is reconciled in a time-dependent Boltzmann description, which allows an attribution of the observed third-harmonic generation to the terahertz field driven nonlinear kinetics of the heavy quasiparticles.},
keywords = {B1, B5},
pubstate = {published},
tppubtype = {article}
}
We report on time-resolved nonlinear terahertz spectroscopy of a strongly correlated ruthenate, CaRuO3, as a function of temperature, frequency, and terahertz field strength. Third-harmonic radiation for frequencies up to 2.1 THz is observed evidently at low temperatures below 80 K, where the low-frequency linear dynamical response deviates from the Drude model and a coherent heavy quasiparticle band emerges by strong correlations associated with the Hund’s coupling. Phenomenologically, by taking an experimentally observed frequency-dependent scattering rate, the deviation of the field driven kinetics from the Drude behavior is reconciled in a time-dependent Boltzmann description, which allows an attribution of the observed third-harmonic generation to the terahertz field driven nonlinear kinetics of the heavy quasiparticles. | |
