On-line SPICE-SPIN+X Seminars

On-line Seminar: 03.06.2026 - 15:00 CET

TBA

Jörn Venderbos, Drexel

TBA

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 15.07.2026 - 15:00 CET

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Daniel F Agterberg, UW

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 06.05.2026 - 15:00 CET

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Marcel Franz, UBC

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 08.04.2026 - 15:00 CET

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Rafael Fernandes, UIUC

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 14.01.2026 - 15:00 CET

Magnetic excitations beyond the single- and double- magnons

Hebatalla Elnaggar , Sorbonne University

Conventional wisdom suggests that one photon that carries one unit of angular momentum (1h) can change the spin angular momentum of a magnetic site with one unit (ΔM = ±1h) at most following the selection rules. This implies that a two-photon process such as 23 resonant inelastic X-ray scattering (RIXS – see Fig. 1a-c) can change the spin angular momentum of a magnetic system with a maximum of two units (ΔM = ± 2h) [1]. Herein we describe a triple-magnon excitation in the altermagnetic system, -Fe2O3, which contradicts this conventional wisdom that only 1- and 2-magnon excitations are possible in a resonant inelastic X-ray scattering experiment [2].

Figure 1: Schematic of Resonant Inelastic X-ray Scattering (RIXS). (a) The initial state of a 3d transition metal plus a photon with energy ℏin, wave-vector kin. (b) The intermediate state where a 2p electron is excited to the empty 3d states leaving a core-hole that exists for few fs. (c) The final state where a valence 3d electron fills the core-hole and a photon with energy ℏout, wave-vector kout is emitted. The energy and momentum transfer are given by ℏ(in - out) and ℏ(kin-kout), respectively. (d) Fe 2p3d RIXS measured in -Fe2O3 single crystal where we observed multi-magnons.

We observe an excitation at exactly three times the magnon energy, along with additional excitations at four and five times the magnon energy, suggesting the presence of quadruple and quintuple magnons as well (see Fig. 1d). Guided by theoretical calculations, we reveal how a two-photon scattering process can create exotic higher-rank magnons and the relevance of these quasiparticles for understanding spin non-conserving interactions where the lattice degree of freedom acts as a reservoir of angular momentum.

References:
[1]- A. Nag, et. al., Many-body physics of single and double spin-flip excitations in NiO, Phys. Rev. Lett., 124, 067202 (2020).
[2]- H. Elnaggar, et. al., Magnetic excitations beyond the single- and double-magnons, Nat. Commun. 14, 2749 (2023).

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 25.02.2025 - 15:00 CET

Emerging Altermagnetism and Polar States in Strained Metallic RuO2 Films

Bharat Jalan , University of Minnesota

Department of Chemical Engineering and Materials Science, University of Minnesota, Twin Cities

RuO2, a rutile 4d-transition metal oxide, exhibits a unique crystal structure with both edge- and corner-sharing octahedra. This intrinsic anisotropy, when combined with strain engineering, provides a powerful avenue for tuning anisotropic electronic and optical properties. However, from a synthesis perspective, challenges such as variable Ru valence states, Ru/O stoichiometry control, anisotropic strain states, and structural defects can make it difficult to distinguish intrinsic properties from extrinsic effects in RuO2 thin films – a classic trick in the pursuit of novel functionalities in quantum materials.

In this talk, I will highlight our group’s efforts in overcoming these synthesis challenges while demonstrating metallicity in epitaxial RuO2 films down to the unit cell scale. Through a combination of advanced X-ray scattering, X-ray absorption spectroscopy, transmission electron microscopy, temperature-dependent transport, magneto-optical measurements, and density functional theory (DFT) calculations, we uncover robust magnetism in epitaxially strained RuO2, consistent with an altermagnetic metallic phase [1-4]. Additionally, we reveal a novel polar phase in strained films with significant implications for electrical transport – an unexpected treat in the realm of functional oxides. I will discuss these findings in detail, emphasizing their sensitivity to material defects and structure – key ingredients that are often overlooked but crucial in determining emergent quantum phenomena.

Reference:

1. S. G. Jeong†, I. H. Choi†, S. Nair, L Buiarelli, B. Pourbahari, J. Y. Oh, N. Bassim, A. Seo, W. S. Choi, R. M. Fernandes, T. Birol, L. Zhao, J. S. Lee, and B. Jalan, Altermagnetic polar metallic phase in ultra-thin epitaxially-strained RuO2 films, (under review) (2025) [arxiv] †Equal contribution
2. S. G. Jeong, I. H. Choi, S. Lee, J. Y. Oh, S. Nair, J. H. Lee, C. Kim, A. Seo, W. S. Choi, T. Low, J. S. Lee, and B. Jalan, Anisotropic Strain Relaxation-Induced Directional Ultrafast Carrier Dynamics in RuO2 Films, Sci. Adv. 11, eadw7125 (2025)
3. S. G. Jeong, S. Lee, B. Lin, Z. Yang, I. H. Choi, J. Y Oh, S. Song, S. W. Lee, S. Nair, R. Choudhary, J. Parikh, S. Park, W. S. Choi, J. S. Lee, J. M. LeBeau, T. Low, and B. Jalan, Metallicity and Anomalous Hall Effect in Epitaxially-Strained, Atomically-thin RuO2 Films, PNAS 122(24) e2500831122
4. S. G. Jeong, B. Y. X. Lin, M. Jin, I. H. Choi, S. Lee, Z. Yang, S. Nair, R. Choudhary, J. Parikh, A. Santhosh, M. Neurock, K. A. Stoerzinger, J. S. Lee, T. Low, Q. Tu, J. M. LeBeau, and B. Jalan, Strain-Stabilized Interfacial Polarization Tunes Work Function Over 1 eV in RuO2/TiO2 Heterostructures, under review (2025) [arxiv]

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 26.11.2025 - 15:00 CET

Novel glimpse into ground states of quantum matter

Vesna Mitrović, Brown University

In this talk I would describe novel in-situ ``interferometry'' technique that is employed to probe ground state properties of the complex materials. Examples of the power of this nuclear magnetic resonance inspired technique will be illustrated on magnetic and frustrated materials.
Specifically, I will show how this technique can be used to sense changes in quantum mechanical ground state wavefunction through a high temperature magnetic phase transition.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 12.11.2025 - 15:00 CET

Superconducting spintronics with magnetically compensated materials

Jacob Wüsthoff Linder, NTNU

Altermagnets have emerged as intriguing materials supporting strongly spin-polarized
currents despite the lack of a net magnetization. We demonstrate that altermagnets
enable several promising functionalities when merged with conventional superconductors.
We predict that altermagnets act as spin-filters for triplet Cooper pairs
and that they can function as cryogenic spin-valves acting as a memory device without stray fields, offering
high storage densities. Finally, we discuss the interplay between p-wave magnetism
and superconductivity both intrinsically in a material and via the proximity effect in a bilayer.
We show that p-wave magnets induce a charge-to-spin conversion in combination with
superconductors that, unexpectedly, is even larger than in the normal state.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 15.10.2025 - 15:00 CEST

Superconductivity in altermagnets

Annica Black-Schaffer, Uppsala University

Altermagnets break spin-degeneracy, as in a ferromagnet, but with a momentum dependent spin splitting resulting in zero net magnetization, as in antiferromagnets. Due to this unique magnetization, altermagnets also produce intriguing possibilities for other ordered phases of matter. Magnetism and superconductivity are two of the most celebrated quantum phases of matter and usually have a ‘friend-foe’ dichotomous relation and combining superconductivity with altermagnetism turns out to open for new exceptional possibilities. In this talk I will show several novel effects occurring when superconductivity appears in altermagnets, including finite momentum pairing, field-induced superconductivity [1], and a perfect superconducting diode effect [2], as well as demonstrate constraints on the superconducting pairing [3]. If time permits, I will also demonstrate the possibility for orbital-selective altermagnetism in the unconventional superconductor Sr2RuO4 [4].

[1] D. Chakraborty and A. M. Black-Schaffer, Zero-field finite-momentum and field-induced superconductivity in altermagnets, Phys. Rev. B110, L060508 (2024).
[2] D. Chakraborty and A. M. Black-Schaffer, Perfect superconducting diode effect in altermagnets, Phys. Rev. Lett. 135, 026001 (2025)
[3] D. Chakraborty and A. M. Black-Schaffer, Constraints on superconducting pairing in altermagnets, Phys. Rev. B 112, 014516 (2025)
[4] C. Autieri, G. Cuono, D. Chakraborty, P. Gentile, and A. M. Black-Schaffer, Conditions for orbital-selective altermagnetism in Sr2RuO4: Tight-binding model, similarities with cuprates, and implications for superconductivity, Phys. Rev. B 112, 014412 (2025)

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 06.08.2025 - 15:00 CEST

Chiral phonons for spintronics

Ulrich Nowak, University of Konstanz

The discovery and investigation of chiral phonons uncovered a variety of novel physical effects which are related to the chiral phonon's angular momentum as well as its associated magnetic field. Their interaction with the electron spin offers opportunities for an exploitation in spintronics, where they can be functionalized as additional carriers for the transport of anular momentum. However, the microscopic understanding of the coupled dynamics of the electronic angular momenta and the lattice degrees of freedom [1] is still incomplete.

This new research field calls for new modelling approaches and numerical tools. In this talk we report on recent developments in the microscopic understanding of the coupling between spin and lattice degrees of freedom with an emphasis on the exchange of angular momentum between these two subsystems. Specifically, we discuss a framework for spin-molecular dynamics that connects, on the one hand, to ab initio calculations of spin-lattice coupling parameters [2,3] and, on the other hand, to the magneto-elastic continuum theory. This framework allows for multi-scale modeling approaches including the development of material-specific atomistic models for the coupled spin and lattice degrees of freedom, the calculation and investigation of magnon-phonon dispersion relations [4], and the development and use of modelling tools for coupled spin-lattice dynamics.

[1] S. R. Tauchert, M. Volkov, D. Ehberger, D. Kazenwadel, M. Evers, H. Lange, A. Donges, A. Book, W. Kreuzpaintner, U. Nowak, P. Baum: Polarized phonons carry angular momentum in ultrafast demagnetization, Nature 602, 73 (2022)
[2] S. Mankovsky, S. Polesya, H. Lange, M. Weißenhofer, U. Nowak, and H. Ebert:
Angula Momentum Transfer via Relativistic Spin-Lattice Coupling from First Principles, Phys. Rev. Lett. 129, 067202 (2022)
[3] M. Weißenhofer, H. Lange, A. Kamra, S. Mankovsky, S. Polesya, H. Ebert, and U. Nowak: Rotationally invariant formulation of spin-lattice coupling in multi-scale modeling, Phys. Rev. B 108, L060404 (2023)
[4] M. Weißenhofer, P. Rieger, M.S. Mrudul, L. Mikadze, U. Nowak, and P. M. Oppeneer: Truly chiral phonons arising fromm chirality selective Magnon-Phonon Coupling, arXiv:2411.03879v1
[5] 2022

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