2024/08/09 by Marius Weber, Stephan Wust, Weber, Marius +30 · 11 citations
Engineering · Physics and Astronomy · #Magneto-Optical Properties and Applications #Magnetic properties of thin films #Atomic and Subatomic Physics Research
paper · pdf · doi:10.48550/arxiv.2408.05187
The recently discovered altermagnets exhibit collinear magnetic order with zero net magnetization but with unconventional spin-polarized d/g/i-wave band structures, expanding the known paradigms of ferromagnets and antiferromagnets. In addition to novel current-driven electronic transport effects, the unconventional time-reversal symmetry breaking in these systems also makes it possible to obtain a spin response to linearly polarized fields in the optical frequency domain. We show through ab-initio calculations of the prototypical d-wave altermagnet RuO2, with a symmetry combining twofold spin rotation with fourfold lattice rotation, [C2‖C4z], that there is an optical analogue of a spin splitter effect, as the coupling to a linearly polarized exciting laser field makes the d-wave character of the altermagnet directly visible. By magneto-optical measurements on RuO2 films of different thicknesses ranging from 2 to 8 nanometers, we demonstrate the predicted connection of the linear polarization of an ultrashort pump pulse to the sign and magnitude of the optically excited electronic spin polarization in the ultrathin RuO2 films. The possibility of exciting and controlling an electronic spin polarization by linearly polarized optical pulses in a compensated system is a unique consequence of the altermagnetic material properties. Our experimental results therefore establish an optical pump-probe based protocol for detection of altermagnetic characteristics in ultrathin RuO2 films, but our all-optical approach should apply more generally to materials in this altermagnetic symmetry class.