On-line SPICE-SPIN+X Seminars

On-line Seminar: 14.01.2026 - 15:00 CET

TBA

Hebatalla Elnaggar , Sorbonne University

TBA

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 17.12.2025 - 15:00 CET

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Bharat Jalan , University of Minnesota

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 26.11.2025 - 15:00 CET

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Vesna Mitrović , Brown University

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 12.11.2025 - 15:00 CET

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Jacob Wüsthoff Linder , NTNU

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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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On-line SPICE-SPIN+X Seminars

On-line Seminar: 25.06.2025 - 15:00 CEST

Magnetism in Moiré Materials

Allan MacDonald , University of Texas

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).

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 16.07.2025 - 15:00 CEST

Superconductivity at interfaces of the quantum paraelectric KTaO3

Anand Bhattacharya, Argonne National Laboratory

In this talk I will discuss the recently discovered two-dimensional superconductivity found at interfaces of the incipient ferroelectric KTaO3 (KTO). In its pristine insulating state, KTO is believed to be a ‘quantum paraelectric’, where the onset of ferroelectricity at low temperatures is thwarted by quantum fluctuations. A metallic electron gas can be obtained at interfaces of KTO by depositing a variety of insulating metal-oxide overlayers. Electron microscopy studies reveal the presence of both oxygen vacancies near the interface of KTO and diffusion of cations into KTO from the oxide overlayers, which dope the interfacial region of KTO with electrons. These interfacial electron gases were found to be superconducting up to temperatures as high has 2.2 K. Remarkably, the superconducting state is orientation selective, where electron gases formed at the (111) and (110) crystalline interfaces of KTO are robust two-dimensional superconductors, with Tc as high as 2.2 K and 1 K respectively, while electron gases formed at the (001) interface of KTO and oxide overlayers remain normal down to 25 mK. In this light, I will present a proposed mechanism for superconductivity at KTO interfaces where pairing involves an inter-orbital coupling mechanism mediated by the same soft phonon that is responsible for the incipient ferroelectricity in KTO. This mechanism favors superconductivity in states with maximal orbital degeneracy, and the lifting of this degeneracy due to quantum confinement effects explains the orientation selective nature of superconductivity at KTO interfaces. The broken inversion symmetry and strong spin-orbit coupling in KTO interfacial electron gases also lead to a spin-textured Fermi surface. I will outline how orbital degeneracy gives rise to a uniaxial ‘in-plane Ising’ spin texture for electron gases formed at KTO (110) interfaces, evidenced by their interaction with an insulating magnetic overlayer in both their superconducting and normal states.

References:
1. C. Liu et al., Science 371, 716 (2021).
2. C. Liu et al., Nature Communications 14, 951 (2023).
3. J. Yang et al., arXiv 2502.19599.

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 29.10.2025 - 15:00 CET

TBA

Ron Naaman, Weizmann Institute of Science

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 09.04.2025 - 15:00 CEST

van der Waals Magnets and Antiferromagnets Interacting with Electron Spins

Daniel Ralph, Cornell University

This talk will discuss two projects. The first concerns topological insulator/magnet samples made by mechanical stacking of exfoliated van der Waals flakes. The proximity interaction of the magnet with the topological surface state allows realization of the “parity anomaly” half-quantized Hall effect state at temperatures as high as 10 K -- the first materials system with a quantized anomalous Hall signal well above liquid-helium temperature. Direct capacitive measurements also indicate a large value of the exchange gap of approximately 10 meV. We speculate the reason for the higher temperature scale compared to previous topological insulator/magnet samples deposited by molecular beam epitaxy is that even a small amount of disorder due to interfacial mixing in deposited samples can push the topological surface state away from the interface and thereby weaken the exchange coupling to the magnet. The pristine interfaces formed by mechanical stacking of van der Waals layers eliminate this intermixing.

The second project concerns 3-terminal tunnel junctions (PtTe2/bilayer CrSBr/graphite) in which the A-type van der Waals antiferromagnet CrSBr acts as the tunnel barrier. Spin-filter tunneling through the CrSBr bilayer allows direct electrical measurements of antiferromagnetic resonance in the frequency domain. Furthermore, spin-orbit torque from the PtTe2 electrode provides electrically-tunable control over the magnetic damping and resonance linewidth. We find the interesting result that the spin-orbit torque is highly local, with the spin current from the PtTe2 electrode acting only on the individual spin sublattice layer adjacent to that electrode, with a negligible amount propagating to the next van der Waals layer.

 

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