Tea in the Atrium Room: 307

Colloquium Room: 307 Title: Excitations of Magnetized Antiferromagnets — Fractionalized Spinons and Dynamic Gauge Fluxes Abstract: Quantum spin liquids—magnetic states characterized by long-range entanglement and fractionalized excitations—challenge the conventional description of antiferromagnets in terms of ordered moments and magnons. In this talk, I revisit the evolution of ideas about the antiferromagnetic ground state, from semiclassical order to resonating valence-bond constructions and parton descriptions with emergent gauge structure, highlighting how these frameworks reshape our understanding of magnetic excitations. I then turn to the two-dimensional Dirac quantum spin liquid, a candidate realization of (2+1)-dimensional quantum electrodynamics with gapless Dirac spinons coupled to an emergent U(1) gauge field. A central question is how such a state responds to an external magnetic field. Recent work reveals an unexpected magnetization process that cannot be understood within conventional spin-wave or quasiparticle pictures. I conclude by outlining a theoretical scenario, supported in part by numerical studies, in which increasing magnetization induces an internal gauge flux. This emergent orbital field reorganizes the spinon spectrum into relativistic Landau levels, providing a novel mechanism for field-driven reconstruction in a fractionalized magnet.