Dresden 2026 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 35: Cooperative Phenomena: Spin Structures and Magnetic Phase Transitions (joint session MA/TT)

TT 35.2: Talk

Tuesday, March 10, 2026, 14:15–14:30, POT/0151

Large magnetoreflectance and optical anisotropy due to 4f flat bands in the frustrated kagome magnet HoAgGe — •Felix Schilberth^1,2, Luke DeFreitas³, Khan Zhao^4,5, Florian Le Mardelé⁶, Ivan Mohelsky⁶, Milan Orlita⁶, Philipp Gegenwart⁵, Hua Chen³, István Kézsmárki¹, and Sándor Bordács² — ¹Experimentalphysik V, Unversity of Augsburg — ²Department of Physics, BME Budapest — ³Department of Physics, Colorado State University — ⁴School of Physics, Beihang University — ⁵Experimentalphysik VI, Unversity of Augsburg — ⁶LNCMI, Université Grenoble Alpes

We report peculiar optical properties of the frustrated itinerant magnet HoAgGe, which exhibits multiple magnetically ordered states obeying the kagome spin-ice rule. The optical conductivity is higher for light polarization perpendicular to the kagome plane both for the free carrier response and the interband transitions. The latter have strong contributions from Ho 4f flat bands located near the Fermi level, as revealed by our ab initio calculations, explaining the unusual anisotropy of the optical properties and the pronounced temperature dependence of the interband transitions for out-of-plane light polarization. The key role of Ho 4f states is further supported by the large variation of the magneto-reflectivity, following the field dependence of the magnetization in contrast to that of the magnetotransport data. Such heavy-electron bands near the Fermi level offer an efficient way to control transport and optical properties and we show that their ultrafast magneto-optical response is susceptible to the magnetic order.

Keywords: Non-collinear Antiferromagnets; Magneto-Optics; Metamagnetic Phases; 4f Electrons; HoAgGe