Events at Physics |
Events on Thursday, September 24th, 2026
- R. G. Herb Condensed Matter Seminar
- Emergent Clock Order and Giant Magnetoelectricity in van der Waals Magnets
- Time: 10:00 am - 11:00 am
- Place: Chamberlin 5310
- Speaker: Frank Gao, UW-Madison Chemistry
- Abstract: Van der Waals magnets provide a fertile setting in which reduced dimensionality, enhanced fluctuations, topology, and strong correlations reshape familiar forms of magnetism. Much of this physics is encoded in subtle changes to the magnetic order parameter — its symmetry, spatial texture, and coupling to other degrees of freedom — that are difficult to resolve with conventional magnetic probes. Here, I will show how symmetry-sensitive nonlinear optical microscopy can unveil these hidden orders and follow their dynamics. I will first discuss NiPS3, where we use second-harmonic generation microscopy to show how reduced dimensionality transforms the material’s bulk antiferromagnetism, giving rise to a six-state clock order emerging from a BKT phase in the monolayer limit. I will then turn to the van der Waals multiferroic NiI2, where chiral magnetism is intimately coupled to ferroelectric polarization. By combining complementary electric- and magnetic-dipole-sensitive nonequilibrium probes, we identify terahertz collective modes with an exceptionally large chiral dynamical magnetoelectric response. Beyond their fundamental implications, these experiments establish new avenues for engineering and manipulating correlated spin systems in atomically thin magnets, with potential applications in spintronics, quantum sensing, and light-driven quantum technologies.
- Host: Elio Koenig-Tarasevich
- Astronomy Colloquium
- Black Hole Images: What they've taught us so far and how we can improve them
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Lia Medeiros, UW-Milwaukee
- Abstract: Horizon-scale observations of accreting supermassive black holes with the Event Horizon Telescope (EHT) have opened a new window onto strong-field gravity and black-hole accretion. The EHT's 2022 observations of Sagittarius A* (Sgr A*), the black hole at the center of our Galaxy, provide a new opportunity to test the Kerr metric in a previously unexplored regime. I will discuss the EHT observations of Sgr A*, focusing on what they can reveal about fundamental physics, and briefly compare these results with the earlier observations of M87*. I will then discuss how improvements in both observations and data analysis can extend these measurements in the near future. In particular, I will introduce PRIMO, a machine-learning algorithm for EHT data analysis that uses a large library of high-fidelity simulations as a training set. I will show a higher-resolution reconstruction of M87* obtained with PRIMO and demonstrate how improved image reconstruction can provide new constraints on both black-hole accretion and strong-field gravity.
- Host: Nicholas Stone
