Speaker
Description
Vortex dynamics in superfluids is strongly affected by the presence of impurities or obstacles that can act as pinning sites. Pinning of quantized vortices inside a neutron star is predicted to play an important role in its rotational dynamics and can lead to sudden changes in angular velocity known as glitches. In a system with a multicomponent order parameter, such as a spin-triplet superfluid expected to form in the core of a neutron star, the interaction between vortices and pinning sites can be more complicated due to the non-trivial structure of the vortex cores. Superfluid $^3$He is a model example of a spin-triplet system where a wide variety of different types of vortices have been observed [1,2], and where pinning sites can be introduced in experiments via nanoscale confinement [3].
We study the structure of vortex cores in superfluid $^3$He using the Ginzburg-Landau formalism, and the problem of a vortex pinned by columnar defects with sizes comparable to the coherence length. We calculate both the depinning velocity and the shape of the energy barrier for the depinning process. The multicomponent nature of the order parameter can lead to fractional depinning, where the vortex detaches from the defect as two half-quantum vortices.
[1] R. Rantanen and V. B. Eltsov, PRR 6, 043112 (2024)
[2] S. Autti et al., PRL 117, 255301 (2016)
[3] S. Autti et al., PRR 2, 033013 (2020)