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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 5.1: Hauptvortrag

Montag, 17. März 2025, 09:30–10:00, H20

Driving Coherent Phonon-Phonon Angular Momentum Transfer via Lattice Anharmonicity — •Sebastian Maehrlein — Fritz Haber Institute of the Max Planck Society — Helmholtz Zentrum Dresden Rossendorf — TU Dresden

The discrete rotational symmetry of crystal structures leads to the conservation of quantized angular momentum in solids. Whereas the exchange of energy and linear momentum between lattice vibrations (phonons) via anharmonic coupling is a cornerstone of solid-state physics, conservation and transfer of angular momentum within the lattice remained a postulate, yet. Recently, phonon angular momentum, often in the form of chiral phonons, was linked to gigantic magnetic fields, dynamical ferroelectricity, ultrafast demagnetization, or magnetic switching. However, the fundamental process of phonon to phonon angular momentum transfer required for demagnetization and other spin-related relaxation phenomena remained elusive.

Here we drive coherent phonon-phonon angular momentum transfer by establishing helical nonlinear phononics. Thereby, we directly observe phonon helicity-switching dictated by (pseudo) angular momentum conservation and the discrete rotational symmetry of the lattice. Ab-initio modeling in conjunction with classical equations of motion confirm the experimentally observed anharmonic phonon-phonon coupling as the dominating lattice angular momentum transfer channel. Our results thus open the field of helical or chiral nonlinear phononics, turning lattice angular momentum into the long missing tuning knob for ultrafast material control.

Keywords: Phonon Angular Momentum; Nonlinear Phononics; High-Field THz Physics; Coherent Phonons; Ultrafast Dynamics