Speaker: Minhyea Lee, Department of Physics, University of Colorado Boulder
Abstract: Magnetic insulators hold great promise for technologies such as spintronics and quantum information processing. These applications rely on the novel functionality of real materials, requiring a thorough understanding of magnetic ground-state properties such as ordering—whether conventional or exotic—, low-energy spin excitations, and interactions between spin and lattice degrees of freedom. Insulating rare-earth magnets are especially suited for this purpose: strong spin–orbit coupling and crystal electric field (CEF) effects produce pronounced anisotropy and competing energy scales that can give rise to magnetic frustration.
In this talk, I will present the highly anisotropic CEF level splittings of Kramers’ rare-earth ions under a magnetic field, observed via direct magneto-optical spectroscopy as well as resonant torsion magnetometry. This reveals unusual ground-state properties, including quadratic field-dependent Zeeman splitting and/or ground-state level crossing. I will then discuss how, in rare-earth magnets, hybridization between acoustic phonons and spin-flip excitations across the Zeeman gap produces unusual field dependence of thermal conductivity. This, in turn, offers insight into a better understanding of magnetic properties across a wide range of rare-earth magnets.
Short Bio: Minhyea Lee is a professor of physics at the University of Colorado Boulder. She earned her PhD at the University of Chicago and held postdoctoral positions at Princeton University and NIST Boulder before joining CU Boulder. An experimental condensed matter physicist, she studies quantum materials, focusing on frustrated magnetism, spin excitations, and spin–lattice coupling. Her group combines transport, thermodynamic, and spectroscopic probes to connect microscopic interactions with macroscopic behavior.
