Regensburg 2025 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 15: Poster I
MA 15.1: Poster
Dienstag, 18. März 2025, 10:00–12:30, P1
Truly Chiral Phonons Arising From Chirality-Selective Magnon-Phonon Coupling — •Philipp Rieger1, Markus Weissenhofer1,2, Luca Mikadze1, M. S. Mrudul1, Ulrich Nowak3, and Peter M. Oppeneer1 — 1Uppsala University, Uppsala, Sweden — 2Freie Universität Berlin, Berlin, Germany — 3Universität Konstanz, Konstanz, Germany
Growing attention has focused on the angular momentum of phonons, particularly in ultrafast magnetization dynamics. This arises from the circular or elliptical motion of atoms around equilibrium positions, forming collective modes known as chiral phonons.
Structural inversion symmetry (P) breaking is well known to give rise to chiral phonons. Here, we present an alternative mechanism for the generation of chiral phonons, stemming from magnon-phonon coupling in P-symmetric crystal lattices with time-reversal symmetry breaking.
We investigate magnon-phonon coupling in bcc Fe using a first-principles framework. Our calculations reveal the hybridization of magnon and phonon modes, giving rise to magnon-polarons and an avoided crossing (energy gap) in the dispersion relations. Along specific high-symmetry lines in reciprocal space, we observe that magnon coupling transforms degenerate transverse phonon modes into chiral phonons, characterized by an energy splitting between left- and right-handed modes. Our findings challenge conventional magneto-elastic interpretations and reveal zero-point phonon angular momentum and anomalous Hall effects linked to finite (spin) Berry curvatures.
Keywords: Phonon Angular Momentum; Chiral Phonons; Ultrafast Magnetism; Spin-Lattice Coupling