Professor Vladimir Eltsov (Dept Applied Physics, Aalto University, Finland)

Superfluid phases of 3He possess unique variety of properties determined by topology in real and momentum spaces. Novel topological phases of this p-wave superfluid can be engineered by placing the fluid into nanostructured confinement. We study experimentally the polar phase of 3He, stabilized between long nm-diameter solid strands. In the momentum space of the polar phase, we demonstrate existence of the Dirac nodal line in the energy spectrum of Bogoliubov quasiparticles and its robustness to disorder introduced by impurities provided by extension of the Anderson theorem [1]. The nodal line reduces Landau critical velocity in the polar phase to zero, but we nevertheless observe stable superflow as the nodal line transforms to topological Bogoliubov Fermi surface under the flow [2]. In the real space of the polar phase, we create half-quantum vortices (HQVs) [3] using in particular the Kibble-Zureck mechanism controlled by a symmetry-breaking bias field [4]. We then transfer HQVs through a sequence of transitions to other superfluid phases [5] to realize composite topological objects suggested by Kibble, Lazarides, and Shafi for cosmological phase transitions.

[1] J. Rysti et al, arXiv:1908.01645.

[2] S. Autti et al, Phys. Rev. Research 2, 033013 (2020).

[3] S. Autti et al, Phys. Rev. Lett. 117, 255301 (2016).

[4] J. Rysti et al, Phys. Rev. Lett. 127, 115702 (2021).

[5] J.T. Mäkinen et al, Nature Commum. 10, 237 (2019).