Speaker
Description
Intermetallics of type R Rh$_2$Si$_2$ (R is a rare earth) are antiferromagnets (AFM) with a Schokley surface state that becomes strongly spin-split in the AFM phase (up to 160 meV split). We study the coupling between the bulk AFM order and the surface spin polarization by probing the ultrafast dynamics of both properties in two complementary techniques. We use resonant X-ray diffraction (trRXD) to study the dynamics of the AFM order at the R ions' M edges, and we observe the narrowing of the spin-splitting gap using XUV time- and angle-resolved photoemission spectroscopy (trARPES). Comparison of the ultrafast demagnetization dynamics of the two orders allows us to address the coupling between them. The AFM dynamics also exhibited a coherent rotation of the entire AFM spin structure. This was resolved by measuring dynamics at several azimuths, which allows us to describe the entire AFM spin structure as a function of time. Lastly, differences in demagnetization timescales between SmRh$_2$Si$_2$ and GdRh$_2$Si$_2$ (∼300 fs vs 11 ps) suggest a strong variation in spin-lattice coupling, in analogy to 4f magnetization dynamics in Lanthanide metals.
