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MA: Fachverband Magnetismus

MA 5: Focus Session: Magnetic Phenomena from Phonon Chirality and Angular Momentum I (joint session MA/TT)

MA 5.5: Invited Talk

Monday, March 17, 2025, 11:45–12:15, H20

Giant effective magnetic moment of chiral phonons — •Swati Chaudhary^1,3, Dominik Juraschek², Martin Rodriguez-Vega³, and Gregory A Fiete⁴ — ¹The Institute for Solid State Physics, The University of Tokyo, Japan — ²Eindhoven University of Technology, Eindhoven, Netherlands — ³The University of Texas at Austin, Austin, USA — ⁴Northeastern University, Boston, USA

Chiral phonons carry angular momentum and lead to magnetic responses in applied magnetic fields or when resonantly driven with ultrashort laser pulses. On the basis of purely circular ionic motion, these phonons are expected to carry a magnetic moment of the order of a few nuclear magnetons. However, some recent experiments have demonstrated a phonon magnetic moment of the order of a few Bohr magnetons. This kind of giant magnetic response points towards the electronic contribution to the magnetic moment of phonons. Many diverse mechanisms have been discovered for this enhanced magnetic response of chiral phonons. The orbital-lattice coupling is one such mechanism where low-energy electronic excitations on a magnetic ion hybridize with phonons and endow a large magnetic moment to phonons. In this talk, I'll present a microscopic model for the effective magnetic moments of chiral phonons based on this mechanism. We apply our model to two types of materials: rare-earth halide paramagnets and transition-metal oxide magnets. In both cases, we find that chiral phonons can carry giant effective magnetic moments of the order of a Bohr magneton, orders of magnitude larger than previous predictions.

Keywords: Magnetism; Chiral phonons; electron-phonon coupling