Seminar: Ultrafast phononic switching of ferroic order

Vibrations of the crystal lattice have a significant impact on the orbital dynamics of the electrons, and through it, on spins. Ultrafast excitation of phonons resulting in drastic repopulation of phononic system was thus shown to be able to modify the fundamental magnetic interactions [1]. And very recently time-resolved X-ray scattering and electron diffraction experiments demonstrated the angular momentum transfer from magnetization to the phonon system, on a femtosecond time scale, dubbed ultrafast Einstein-de-Haas effect [2,3]. It should therefore be possible to realize the opposite process, by changing the lattice and thus controlling the magnetization, on the same time scale – in femtoseconds!

To confirm this, we have recently shown how the resonant excitation of circularly-polarized optical phonons in paramagnetic substrates can permanently reverse the magnetic state of the overlayer [4]. The helicity-dependence of the switching implies that the lattice vibrations excited in the substrate deliver a directional field that pushes the magnetization towards a switched or non-switched state. The nature of such field is however rather unknown and is a topic of debate.

Moreover, a different behaviour, characterized by displacive modification of crystal potentials, is driven by linearly-polarized excitation. The magnetic switching was shown to create very peculiar quadrupolar spatial domain patterns [5], confirming the mechanism. The mechanism appears to be ultimately universal, as observed in variety of systems, not only magnetic ones [6]. The dynamics of the domain formation was shown to proceed via a strongly inhomogeneous magnetic state resulting in a self-organization of magnon-polarons [7] and formation of magneto-elastic solitons.

1. S. F. Maehrlein et al, Science Adv. 4, eaar5164 (2018).
2. C. Dornes et al, Nature 565, 209 (2019).
3. S. R. Tauchert et al, Nature 602, 73 (2022).
4. C. S. Davies, F. G. N. Fennema, A. Tsukamoto, I. Razdolski, A. V. Kimel & A. Kirilyuk, Nature 628, 540 (2024).
5. A. Stupakiewicz, C. S. Davies, K. Szerenos, D. Afanasiev, K. S. Rabinovich, A. V. Boris, A. Caviglia, A. V. Kimel, & A. Kirilyuk, Nature Phys. 17, 489 (2021).
6. M. Kwaaitaal, D. G. Lourens, C. S. Davies & A. Kirilyuk, Nature Phot. 18, 569 (2024).
7. M. Gidding, T. Janssen, C. S. Davies & A. Kirilyuk, Nature Commun. 14, 2208 (2023).