Dresden 2026 – scientific programme

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MA: Fachverband Magnetismus

MA 8: Altermagnets II

MA 8.9: Talk

Monday, March 9, 2026, 17:15–17:30, HSZ/0002

Optical phonons as a testing ground for spin group symmetries — Felix Schilberth¹, Mark Kondákor⁴, Denis Ukulov², Lilian Prodan¹, Alexander Tsirlin³, Peter Lemmens², Karlo Penc⁴, Istvan Kézsmárki¹, and •Joachim Deisenhofer¹ — ¹Experimental Physics V, Center for Electronic Correlations and Magnetism, Institute for Physics, University of Augsburg, D-86159 Augsburg, Germany — ²Institute of Condensed Matter Physics, TU Braunschweig, Mendelssohnstr. 3, 38106 Braunschweig, Germany — ³Felix Bloch Institute for Solid-State Physics, Leipzig University, 04103 Leipzig, Germany — ⁴Institute for Solid State Physics and Optics, HUN-REN Wigner Research Centre for Physics, H-1525 Budapest, P.O.B. 49, Hungary

We present a detailed study of the infrared- and Raman-active modes in the collinear antiferromagnet and altermagnet candidate Co₂Mo₃O₈. Comparing to ab initio calculations accurately capturing the eigenfrequencies, we identify all expected phonon modes at room temperature and deduce their selection rules with the magnetic point group and the spin group. We observe the change of selection rules upon antiferromagnetic ordering, agreeing with the relativistic symmetry approach, while the spin group formalism predicts no changes. Therefore, optical phonons sensing the symmetry of the magnetic order can reveal if relevant magnon-phonon coupling is compatible with the spin-group approach or not.

Keywords: Altermagnets; Spin groups; Magnetic point group; Magnetolectric; Phonons