Phasons, magnon-polarons and altermagnetic surfaces

DIPC Seminars

Speaker

Wulf Wulfhekel
Karlsruhe Institute of Technology

When

2026/10/09
12:00

Place

DIPC Josebe Olarra Seminar Room

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Magnetic excitations are at the heart of the dynamics of spin systems. Here, we report on the first observation of two magnetic excitations, i.e., magnetic phasons in non-collinear spin textures and magnon-polarons resulting from coupling of acoustic phonons and magnons, and discuss the electronic reorganization near a surface of an altermagnet.
The nanoscopic magnetic texture forming in a monolayer of Fe/Ir(111) is spatially modulated and uniaxially incommensurate with respect to the atomic lattice. As a
consequence, a low-energy magnetic excitation is expected that corresponds to the sliding of the texture along the incommensurate direction, i.e., a phason mode. Using spin-polarized STM, the phason has been experimentally observed and can be excited by the tunneling current.
Fe3GeTe2 (FGT) is a ferromagnetic van der Waals material that hosts collective excitations in form of magnons and phonons at the same time. We study the dynamic coupling of magnons and acoustic phonons in FGT using STM at ultra-low temperatures. A strong interaction between magnons and acoustic phonons leads to avoided band crossings and hybridization between the magnonic and phononic bands, which lifts the constrains set by the selection rules for their individual excitation by electrons and boosts the excitation cross sections. Our findings provide a platform for designing the properties of dynamic magnon-phonon coupling in two-dimensional materials in form of phonon-localization in magnetic domain walls or magnon localization by strain fields.
Finally, we investigated the surfaces of g-wave altermagnets with STM finding substantial tendencies for electronic reorganization, coupling the electronic and lattice degrees of freedom. Investigating the specific symmetries of different surfaces, we conclude that many of the low index surfaces undergo reorganization to a simple Kramers degenerate band structure, while others reduce the symmetry of the altermagnets to d-wave order.