PUB - Publikationen an der Universität Bielefeld

Altermagnets constitute an emerging materials platform for spintronic technologies by combining compensated magnetic order with ferromagnet like spin-split electronic bands. Here, we investigate the proposed d-wave altermagnetic material RuO ₂ using circularly polarized ultrashort laser pulses. Time-resolved magneto-optical Kerr effect measurements, which are intrinsically sensitive to surface and interface states, reveal the ultrafast spin response of RuO ₂ . In contrast to the demagnetization dynamics characteristic of conventional ferromagnets, we observe a distinct coherent contribution to the complex Kerr rotation that appears during the light–matter interaction and lasts for ∼ 200 fs. Similar signatures have been associated with spin–momentum locking and directional band splitting in spin-split surface states of topological insulators as well as spin–orbit–coupled semiconductors and are governed by a finite Raman coherence time. We interpret this coherent response as evidence for transient spin-polarized surface states in RuO ₂ , consistent with the emergence of altermagnetic surface states that are directly relevant to spin-polarized transport at surfaces and interfaces.