Condensed Matter Seminar: Professor Mathias Kläui, Johannes Gutenberg University

Professor Mathias Kläui, of the Institute of Physics, Johannes Gutenberg University, Mainz, will be presenting a seminar on his research. All are welcome to attend.

Topological Spin Dynamics for GreenIT Abstract: In our information-everywhere society IT is a major player for energy consumption. Novel spintronic devices can play a role in the quest for GreenIT if they are stable and can transport and manipulate spin with low power. Devices have been proposed, where switching by energy-efficient approaches, such as spin-polarized currents is used [1], for which we develop new highly spin-polarized materials and characterize the spin transport using THz spectroscopy [2].

Firstly to obtain ultimate stability of states, topological spin structures that emerge due to the Dzyaloshinskii-Moriya interaction (DMI) at structurally asymmetric interfaces, such as chiral domain walls and skyrmions with enhanced topological protection can be used [3-5]. We have investigated in detail their dynamics and find that it is governed by the topology of their spin structures [3]. By designing the materials, we can even obtain a skyrmion lattice phase as the ground state of the thin films [4].

Secondly, for ultimately efficient spin manipulation, we use spin-orbit torques, that can transfer more than 1ħ per electron by transferring not only spin but also orbital angular momentum. We combine ultimately stable skyrmions with spin orbit torques into a skyrmion racetrack device [4], where the real time imaging of the trajectories allows us to quantify the novel skyrmion Hall effect [5].

Finally to obtain efficient spin transport, we study graphene and low damping ferro- and antiferromagnetic insulators as spin conduits. We find very long distance spin transport in the diffusive regime [7] and study coherent superfluid transport [8] that can be controlled in a magnon transistor [9].

[1] Reviews: O. Boulle et al., Mater. Sci. Eng. R 72, 159 (2011); G. Finocchio et al., J. Phys. D: Appl. Phys. 49, 423001 (2016); K. Everschor-Sitte et al., J. Appl. Phys. 124, 240901 (2018). [2] Z. Jin et al., Nature Phys. 11, 761 (2015). [3] F. Büttner et al., Nature Phys. 11, 225 (2015). [4] S. Woo et al, Nature Mater. 15, 501 (2016). [5] K. Litzius et al., Nature Phys. 13, 170 (2017). [6] S. Geprägs et al., Nature Commun. 7, 10452 (2016). [7] R. Lebrun et al., Nature 561, 222 (2018) [8] Y. Tserkovnyak and M. Kläui, Phys. Rev. Lett. 119, 187705 (2017) [9] J. Cramer et al., Nature Commun. 9, 1089 (2018)

Host: Dr Satoshi Sasaki