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MA: Fachverband Magnetismus
MA 54: Spin: Transport, Orbitronics and Hall Effects II
MA 54.8: Vortrag
Donnerstag, 19. März 2020, 17:00–17:15, HSZ 403
Excitation of spin superfluids in easy-plane magnets — •Martin Evers and Ulrich Nowak — University of Konstanz, D-78457 Konstanz
It is long known that easy-plane magnets exhibit an order parameter with SO(2) symmetry, which is equivalent to the U(1) gauge symmetry of the macroscopic wave function of a Bose condensate. For small out-of-plane components the magnetic equations take then a form similar to the Gross-Pitaevski equation, describing the time evolution of a Bose condensate and, hence, superfluidity. Because of this very resemblance, there is a specific type of transport in such magnets called “spin superfluidity” [1-2]. It is characterized by a well defined precession frequency ω0 for all spins and a spin accumulation that spans under ideal conditions over the entire magnet. ω0 basically sets the strength of the spin-superfluid excitation, addressed in this talk.
In a first step we analytically estimate ω0 of spin superfluids in easy-plane ferro- and antiferromagnets. The next step is use atomistic spin simulations to investigate the excitation with respect to changes in the driving strength and the geometry not covered by the analytical theory. We find that in particular the exact geometry of the excited magnet does play a major role on the resulting spin-superfluid response. However, ferro- and antiferromagnets behave in almost aspect very much alike, expect for a lower spin accumulation in antiferromagnets. [3]
[1] B. I. Halperin et al., Phys. Rev. 188, 898 (1969)
[2] S. Takei et al., Phys. Rev. Lett. 112, 227201 (2014)
[3] M. Evers et al., arXiv: 1911.12786