Simultaneous two-color absorption dynamics in the van der Waals ferromagnet FeGeTe
Source: PubMed Central Open Access, NCBI / U.S. National Library of Medicine
For the integration of two-dimensional materials in future devices, a fundamental understanding of their response to external stimuli is needed. Toward this goal, we have investigated the electron and spin dynamics in the metallic van der Waals material FeGeTe(FGT) in its paramagnetic state after ultrafast optical excitation. To this end, we have employed a zone plate streaking technique with probing energies in the extreme ultraviolet range, tuned to the Fe Mand Te Nabsorption edges. This approach provides insights into energy-dependent charge dynamics with a sensitivity to transient absorption changes on the order of. We find a slow carrier relaxation time at both elemental edges—up toin Te and exceeding several picoseconds in Fe—which is surprising for a metal. To elucidate the complex time-resolved response, we also employ static x-ray absorption spectroscopy at the corresponding elemental edges, in which we find a double feature at the Fe Medge. We attribute this to different Fe sites in the pristine material and an oxidized surface layer, and we propose that the time-resolved absorption dynamics show a mixture of signals stemming from the different species. Additionally, we conducted time-resolved x-ray magnetic circular dichroism measurements in FGT at room temperature. We do not find clear evidence of the previously observed light-induced ferromagnetic order above. Our study lays the groundwork for a deeper understanding of charge and spin dynamics in FGT after optica
Abstract
For the integration of two-dimensional materials in future devices, a fundamental understanding of their response to external stimuli is needed. Toward this goal, we have investigated the electron and spin dynamics in the metallic van der Waals material FeGeTe(FGT) in its paramagnetic state after ultrafast optical excitation. To this end, we have employed a zone plate streaking technique with probing energies in the extreme ultraviolet range, tuned to the Fe Mand Te Nabsorption edges. This approach provides insights into energy-dependent charge dynamics with a sensitivity to transient absorption changes on the order of. We find a slow carrier relaxation time at both elemental edges—up toin Te and exceeding several picoseconds in Fe—which is surprising for a metal. To elucidate the complex time-resolved response, we also employ static x-ray absorption spectroscopy at the corresponding elemental edges, in which we find a double feature at the Fe Medge. We attribute this to different Fe sites in the pristine material and an oxidized surface layer, and we propose that the time-resolved absorption dynamics show a mixture of signals stemming from the different species. Additionally, we conducted time-resolved x-ray magnetic circular dichroism measurements in FGT at room temperature. We do not find clear evidence of the previously observed light-induced ferromagnetic order above. Our study lays the groundwork for a deeper understanding of charge and spin dynamics in FGT after optical excitation as part of a roadmap for 2D spintronics.