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Spirals and Skyrmions in Magnets and Their Emergent Electromagnetism
Speaker Dr. Max Hirschberger, The University of Tokyo
Date 25 February 2021 (Thursday)
Time 11:00 - 12:30
Venue Online (Zoom)

Spirals and skyrmion textures are complex magnetic states in solids which, through coupling to the Fermi sea, may generate fascinating non-dissipative electromagnetic responses. A unified description is currently being developed through the concept of quantum-mechanical Berry curvature, in this case corresponding to an emergent magnetic field Ωk living in reciprocal space (k-space).

We used extensive material search, as well as transport and resonant x-ray scattering experiments, to identify a new, centrosymmetric family of rare earth intermetallics with spirals and skyrmion spin-vortices of very short characteristic length scale (<5 nanometers) [1,2].

In the model compound Gd2PdSi3, Ωk is shown to arise from a combination of canted spin texture and degeneracies in k-space [3]. Moreover, spin-dynamics induced by an applied AC current in the related Gd3Ru4Al12 generate a phase-shifted voltage. This emergent inductance grows as the lateral dimensions of the sample become smaller and smaller – contrary to the case of, e.g., a classical coil-based inductor [4].

[1] T. Kurumaji et al., Science 365, 914-918 (2019)
[2] M.H. et al., Nat. Commun. 10, 5831 (2019)
[3] M.H. et al., Phys. Rev. Lett. 125, 076602 (2020)
[4] T. Yokouchi et al., Nature 586, 232–236 (2020)


Max Hirschberger obtained his Ph.D. degree from Princeton University in 2017 under the supervision of Phuan Ong. His work on the thermal Hall effect of magnetic insulators, and on the thermoelectric properties of Weyl semimetals, was recognized with the Kusaka Memorial Prize of Princeton’s Department of Physics and with a Joseph Taylor Graduate Fellowship.

He joined Yoshinori Tokura’s group at RIKEN Center for Emergent Matter Science – close to Tokyo, Japan – as a Postdoctoral Researcher three years ago, with a focus on complex magnetism and its interplay with conduction electrons. Since December 2019, he holds a joint appointment as a Lecturer at the University of Tokyo and as an independent PI at RIKEN.

Meeting Link: To request for meeting link, please write to phweb@ust.hk.