Add to Calendar 2026-11-10T10:00:00 2026-11-10T11:00:00 Ultrafast Control of Spins, Waves and Interactions in Magnetic Materials Event Information: Ultrafast control of magnetisation by light offers a promising route toward energy-efficient information technologies operating on intrinsic magnetic timescales. By engineering the temporal, spectral and polarisation properties of ultrashort light pulses, one can launch the precessional motion of spins, manipulate the magnetic phases and drive the magnetic order far from equilibrium. My research pursues “on-demand” control of magnetism, based on selective perturbing microscopic interaction parameters, which can be used to transform materials into a desired magnetic state.I will first discuss the potential of intense THz-radiation to switch spins in magnetic materials [1-3]. When the strength of the THz field is enhanced with the help of custom-made plasmonic antennas, we achieved switching between stable antiferromagnetic states. In this way the magnetic recording at THz clockrates is made feasible.Then I will show that strong ultrafast driving of infrared active phonons in magnetic materials can also provide a new route to control magnetic properties by triggering coherent magnon oscillations or even inducing a transient magnetic phase not accessible by adiabatic changes of ambient conditions [4].Finally, I will demonstrate that ultrafast excitation does not only switch magnetisation, but also generates the microscopic waves of spin motion inside a magnet, quanta of which are called magnons. The trick to generating magnons at the nanoscale is in the high photon energy of the light pulse. The magnetic material under study exhibited extremely strong absorption of ultraviolet light, which localized the excitation to a very thin region of only a few tens of nanometres from the interface, allowing coherent magnons with 10 nm wavelengths to be generated and controlled [5-7]. [1] S. Baierl, et al. Nature Photonics 10, 715 (2016).[2] S. Schlauderer, et al. Nature 569, 383 (2019).[3] R. Leenders, et al. Phys. Rev. Lett. 135, 246703 (2025).[4] D. Afanasiev, et al. Nature Materials 20, 607 (2021).[5] J. Hortensius, et al. Nature Physics 17, 1001 (2021).[6] R. Leenders, et al. Nature 630, 335 (2024).[7] V. Radovskaia, et al. Nature Physics 22, 728 (2026). Event Location: BRIM 311

Add to Calendar 2026-11-26T10:00:00 2026-11-26T11:00:00 X-ray Spectroscopy of Many-Body States and Interactions Event Information: Many-body systems host states where many different degrees of freedom are intertwined. This makes them exceptionally difficult to investigate, but also gives unprecedented opportunity to control energy and information transfer across chemical and physical states. In this talk, I will show some recent efforts to study and control these interactions leveraging the technique of resonant inelastic X-ray scattering (RIXS). In the first part of the talk, I will show our discovery of intertwined interactions between plasmons and high-order phonons in the layered copper oxides [1,2]. These hybrid modes may have important implications for high temperature superconductivity, but also can be potentially useful as quantum transducers and parametric converters. In the second part of the talk, I will discuss how RIXS revealed a new chemical paradigm to construct Kondo insulators [3], correlated systems where the charge and spin gap arise from many-body Kondo interactions. Subsequently, we studied the dynamics of this many-body system under perturbation, using an optical-pump RIXS-probe method at an FEL [4]. [1] K.-J. Xu et al. Strongly-coupled hybrid lattice-plasmons in layered cuprates. arXiv:2605.29100 (2026).[2] K.-J. Xu et al. Selective coupling of high-order phonons in La2-xSrxCuO4. arXiv:2609.08076 (2026).[3] K.-J. Xu et al. Spectroscopic evidence for a molecular orbital Kondo insulator. arXiv:2605.30293 (2026).[4] K.-J. Xu et al. Persistent photo-enhancement of molecular orbital excitations in the Kondo insulator FeSb2. arXiv: 2610.27630 (2026).  Event Location: BRIM 311