arXiv subjects

Holger Grisk

Publications and source records attributed to Holger Grisk.

3 recordsLinked to original sources

arXiv2026

Femtosecond all-optical coherent control of spin polarization in altermagnets

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 RuO2 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 RuO2. 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 about 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. They are governed by a finite Raman coherence time. We interpret this coherent response as evidence for transient spin-polarized surface states in RuO2, consistent with the emergence of altermagnetic surface states that are directly relevant to spin-polarized transport at surfaces and interfaces.

cond-mat.other↗

arXiv2025

Spin Accumulation based deep MOKE Microscopy

Magnetic imaging techniques are widespread critical tools used in fields such as magnetism, spintronics or even superconductivity. Among them, one of the most versatile methods is the magneto-optical Kerr effect. However, as soon as light is blocked from interacting with the magnetic layer, such as in deeply buried layers, optical techniques become ineffective. In this work, we present a spin-accumulation based magneto-optical Kerr effect (SA-MOKE) microscopy technique that enables imaging of a magnetic thin-films covered by thick and opaque metallic layers. The technique is based on the generation and detection of transient spin-accumulations that propagate through the thick metallic layer. These spin-accumulation signals are directly triggered and detected optically on the same side, lifting any substrate transparency requirements. The spin-accumulation signals detected on a Cu layer decay with a characteristic length of 60 nm, much longer than the 12 nm optical penetration depth, allowing for detection of magnetic contrast with Cu capping layers up to hundreds of nm. This method should enable magnetic imaging in a wide-range of experiments where the surface of interest is covered by electrodes.

cond-mat.mes-hall↗

arXiv2025

Femtosecond photocurrents by the Dresselhaus bulk spin-galvanic effect in an inversion-asymmetric ferromagnet

We study ultrafast photocurrents in thin films of a model ferromagnetic metal with broken bulk inversion symmetry, the half-metallic Heusler compound NiMnSb, following excitation with an optical pump pulse with photon energy 1.55 eV. Remarkably, in terms of the direction of the sample magnetization M, all photocurrents are found to be a superposition of a component with Rashba- and Dresselhaus-type symmetry. We explain the Dresselhaus bulk photocurrent as follows: Pump-induced electron heating induces an excess of spin {\mu}_s||M, which transfers spin angular momentum into states with Dresselhaus-type spin-momentum locking. The resulting charge current relaxes on a time scale of 10 fs by momentum relaxation and, thus, follows {\mu}_s quasi-instantaneously. The relaxation of {\mu}_s is governed by the cooling of the electrons and not by the significantly slower spin-lattice relaxation of half-metals. Our findings add the Dresselhaus spin-galvanic effect (SGE) to the set of ultrafast spin-charge-conversion phenomena. They indicate a route to more efficient spintronic terahertz emitters and detectors based on the volume scaling of the bulk SGE.

cond-mat.mtrl-sci↗