November 16, 1:25 PM, PAN 110
Zoom: https://umn.zoom.us/j/97640459154?pwd=WjlpbmJUQUcxT2txMWM2SnNxSm8rQT09
Prof. Martin Mourigal (Georgia Tech)
One of the scientific frontiers in quantum magnetism is the discovery and understanding of quantum entangled and topologically ordered states in real bulk materials. At the focal point of the experimental investigation of these quantum spin networks is the identification of fractionalized excitations in transport and spectroscopic measurements. Inelastic neutron scattering has proved a powerful technique to reveal such signatures in a variety of systems ranging from quasi-1D magnets to kagome compounds and more. Recent and on-going developments with neutron scattering instrumentation have allowed the characterization of magnetic excitations in entire volumes of momentum-energy space with high resolution. This has prompted revisiting long overlooked materials in search for exotic spin dynamics despite seemingly classical magnetically ordered ground-states. In essence, the venerable Heisenberg model remains a formidably fertile testbed to understand the quantum dynamics of matter and search for magnetic excitations beyond the single magnon paradigm. In this talk, I will discuss such experiments on a long-known material, FeI 2 , and show how high-fidelity modeling brings new insights on the quantum spin dynamics of large-spin systems [1]. I will describe the mechanism that endows low energy quadrupolar fluctuations in FeI 2 with large spectral weight and how these can be completely understood using a SU(3) representation of spin degrees of freedom. I will discuss the consequence of the having several quasiparticles as the low-energy degrees of freedom including formation of heavy bound-states [2] and their mutual decay [3] as a function of applied magnetic field. The talk will offer an imperfect pedagogical analogy between the physics of FeI 2 and the problem of neutrino flavor and oscillations in particle physics. Finally, I will discuss how flat bands in condensed matter systems (here, heavy magnon states) is a fertile ground to understand the stability and sensitivity to interactions of quantum entangled magnetic
states.