On-line SPICE-SPIN+X Seminars

On-line Seminar: 17.12.2025 - 15:00 CEST

TBA

Bharat Jalan , University of Minnesota

TBA
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On-line SPICE-SPIN+X Seminars

On-line Seminar: 26.11.2025 - 15:00 CEST

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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 CEST

TBA

Jacob Wüsthoff Linder , NTNU

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 15.10.2025 - 15:00 CEST

TBA

Annica Black-Schaffer , Uppsala University

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 06.08.2025 - 15:00 CEST

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Ulrich Nowak , University of Konstanz

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On-line SPICE-SPIN+X Seminars

On-line Seminar: 25.06.2025 - 15:00 CEST

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Allan MacDonald , University of Texas

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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.

On-line SPICE-SPIN+X Seminars

On-line Seminar: 29.10.2025 - 15:00 CEST

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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PDF file of the talk available here

On-line SPICE-SPIN+X Seminars

On-line Seminar: 21.05.2025 - 15:00 CEST

Quantum Sensing of Broadband Spin Dynamics and Magnon Transport in Antiferromagnets

P. Chris Hammel, Ohio State University

Optical detection of magnetic resonance using quantum spin sensors (QSS) provides a spatially local and sensitive technique to probe spin dynamics in magnets. However, its utility as a probe of antiferromagnetic resonance (AFMR) remains an open question. We report the first experimental demonstration of optically detected AFMR in layered van der Waals antiferromagnets (AF) up to frequencies of 24 GHz. We leverage QSS spin relaxation due to low-frequency magnetic field fluctuations arising from collective dynamics of magnons excited by the uniform AFMR mode. First, through AFMR spectroscopy we characterize the intrinsic exchange fields and magnetic anisotropies of the AF. Second, using the localized sensitivity of the QSS we demonstrate magnon transport over tens of micrometers. Finally, we find that optical detection efficiency increases with increasing frequency. This showcases the dual capabilities of QSS as detectors of high frequency magnetization dynamics and magnon transport, paving the way for understanding and controlling the magnetism of antiferromagnets.

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