Although numerous solid-state platforms are being developed for quantum applications significant challenges remain with respect to control and scalability, making the development of new qubit technologies a foundational activity pursued intensely. An under-explored platform – nanomagnets – is rapidly demonstrating unique features that could further invigorate the advancement of quantum technologies. This workshop aims to discuss the quantum aspects of tailored magnetic platforms, whose main advantage lies in the high degree of control in manipulation, preparation, parameter tunability, and all-magnetic device integration. It will also discuss some of the recent demonstrations of quantum operations using magnets, the discovery of materials with direct relevance to quantum technology, and the development of sensors able to detect magnetic signals with quantum sensitivity. The event will present the state-of-the-art and opportunities for synergy between quantum technology and tailored spin structures, which holds exciting promise for the creation and preservation of quantum information by magnetic quantum states.
Characterization and control of quantum materials with optical vortex beams
The fascinating physics of optical vortices, in particular light carrying orbital angular momentum (OAM), has resulted in a large interest and currently OAM light can be generated with high precision in a wide photon energy range. Consequently, also the interplay between optical vortices and matter has been investigated in a broad range of phases, from atoms and molecules to solids and plasmas. For example, the study of optical transitions in semiconductors nicely showed the increased complexity of the allowed optical transitions and how the OAM is transferred to the system. This workshop aims to take this a step further and explore how optical vortices can be used to characterize and control complex quantum materials. Through this workshop, it is foreseen to form and bring together a community and form an overview of current and future research endeavors.
Given the exploratory character, the scope of the workshop is purposely kept broad and topics can include, but are not limited to, the following:
• interaction of vortex beams with quantum condensates
• interaction/coupling of the Berry phase associated with the optical OAM vortex with the topological Berry phase in condensed matter
• inducing quantum phase transitions with OAM
• measuring and driving hidden order with vortex beams
• generation and characterization of chiral bosonic modes
Quantum Geometry and Transport of Collective Excitations in (Non-)Magnetic Insulators
Quantum geometric properties of band structures and their signatures in experiments have driven condensed matter research over the past decades. This SPICE workshop will focus on recent theoretical and experimental advances in the topological properties of bands formed by magnetic and hybrid bosonic excitations. While the topology of electron bands is well understood, with unambiguous experimental tools to probe theoretical predictions, their bosonic analogs pose challenges. Although bosonic topological excitations, such as magnon Chern bands, Weyl and Dirac semimetals, and nodal-line semimetals have emerged, the lack of quantized responses and the ambiguity of thermal Hall and Nernst effects prevent their distinct experimental identification. Furthermore, traditional spectroscopic methods for resolving bosonic modes, such as inelastic neutron scattering, lack the contrast to resolve topological boundary states. One possible route to bring the topological excitations under control is to make use of highly tunable platforms, such as magnonic crystals and stacked van der Waals layers. Additionally, the ease of hybridization of magnonic excitations with phonons, photons, and plasmons can provide novel opportunities to directly probe the topological fingerprint.
With this workshop, we aim to provide a forum where experts and students can discuss the latest developments, challenges, and future directions in topological magnetism. Some exciting challenges that we aim to address include:
-Identify direct experimental signatures for topological bosonic excitations
-Explore the impact of many-body interactions on the quantum geometry of the single particle spectrum and transport
-Identify the microscopic origins of thermal Hall conductivity in magnetic and non-magnetic insulators
-Engineer the quantum geometry and topology of collective excitations by non-Hermitian, non-equilibrium, and Floquet control
Magnetic excitations beyond the single- and double- magnons
Hebatalla Elnaggar, Helmholtz Center Berlin
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 ℏin, 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 ℏout, 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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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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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)
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
Two-dimensional van der Waals crystals that are overlaid with a difference in lattice constant or a relative twist form a moiré pattern. In semiconductors and semimetals, the low-energy electronic properties of these systems are accurately described by Hamiltonians that have the periodicity of the moiré pattern creating artificial crystals with lattice constants on the 10 nm scale. Recent progress in fabricating two-dimensional material devices has made it possible to use moiré patterns to design quantum metamaterials in which electrons exhibit strongly-correlated and topologically non-trivial properties that are rare in naturally occuring crystals. Since the miniband widths in both graphene and TMD moiré materials can be made small compared to interaction energy scales (by mechanisms [1,2] that differ), these materials can be used both for quantum simulation and for quantum design. An important property of moiré materials is that their band filling factors can be tuned over large ranges without introducing chemical dopants, simply by using electrical gates.
In this talk I will focus on magnetism in moiré materials, which is sometimes similar to that found in atomic scale crystals and sometimes unusual. In many cases the magnetic order is purely orbital – opening the door to electrical manipulation of magnetic states. Orbital magnetic order combined with non-trivial topology in single-particle bands [3] helps to make quantum anomalous Hall effects common and gives rise to the fractional quantum anomalous Hall effect. The role of band topology is natural in graphene moirés, where it derives from the interesting band topology of graphene monolayers, but has been an unexpected bonus [3] in the case of TMD moires where it derives from the layer degree of freedom.
[1] R. Bistritzer, and A.H.MacDonald, Proceedings of the National Academy of Sciences 26, 12233 ( 2011).
[2] F. Wu, T. Lovorn, E. Tutuc, and A.H.MacDonald, Phys. Rev. Lett. 121, 026402 (2018).
[3] F. Wu, T. Lovorn, E. Tutuc, I. Martin, and A.H.MacDonald, Phys. Rev. Lett. 122, 086402 (2019).
