Femto- phono- magnetism
Sangeeta Sharma
Max-Born-Institute Berlin, Germany
16:15 - 17:15 Tuesday 31 May 2022 Video: https://tugraz.webex.com/meet/schultze From the outset of research into femtomagnetism, the field in which spins are manipulated by light on femtosecond or faster time scales, several questions have arisen and remain highly debated: How does the light interact with spin moments? How is the angular momentum conserved between the nuclei, spin, and angular momentum during this interaction? What causes the ultrafast optical switching of magnetic structures? What is the ultimate time limit on the speed of spin manipulation? What is the impact of nuclear dynamics on the light-spin interaction?
In my talk I will advocate a parameter free ab-initio approach to treating ultrafast light-matter interactions, and discuss how this approach has led both to new answers to these old questions but also to the uncovering of novel and hitherto unsuspected early time spin dynamics phenomena [1,2]. In particular I will show that selective excitation of optical phonon modes exert a strong influence on femtosecond demagnetisation, generating an additional loss of moment within 40 femtoseconds in laser pumped materials. Amongst the available modes that could be optically excited, we identify a strong spin-phonon coupled mode that dominates the early spin dynamics. Underpinning this enhanced loss of moment we deduce a new physical mechanism of inter-site charge transfer, dominant in the minority channel. Our finding demonstrates that the nuclear system, typically assumed to play a role of an energy sink aiding remagnetization of the spin system, can play a profound role in controlling femtosecond demagnetization of magnetic materials.
[1] J. K. Dewhust et al., Nano Lett. 18, 1842 (2018).
[2] Siegrist et al. Nature 571, 240 (2019)
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