Superfluid time crystals

Superfluid time crystals
Vladimir Eltsov, Aalto University
Vladimir Eltsov
Date and time: Thu, Feb 25, 2021 - 11:30am
Category: Condensed Matter Seminar

In superfluid 3He at ultra-low temperatures, spin-wave excitations (magnon quasiparticles) can live for minutes. We create a 3-dimensional trap for magnons within the superfluid and inject sufficient density of magnons with a short pumping pulse, so that later magnons form a Bose-Einstein condensate at the ground level of the trap. Magnon BEC is manifested by spontaneously emerging coherent spin precession, which breaks continuous time translation symmetry and satisfies criteria of a time crystal [1]. We have observed a Nambu-Goldstone mode in the magnon BEC (phonon in a time crystal) [2], the Josephson effect originating in spin superfluidity of two interacting condensates [3], and have simulated Q-balls from high-energy physics with propagating BEC droplets [4]. Additionally, long coherence times have turned magnon condensates into ultra-sensitive probes of relaxation sources in studies of topological objects and various bosonic and fermionic excitations in topological superfluid 3He.

[1] S. Autti et al, Phys. Rev. Lett. 120, 215301 (2018).
[2] S. Autti et al, Phys. Rev. Lett. 121, 025303 (2018).
[3] S. Autti et al, Nature Mater. 20, 171 (2021).
[4] S. Autti et al, Phys. Rev. B. 97, 014518 (2018).