Hiromitsu Takeuchi (Osaka City University) gives a webinar on “Topological defects in easy-axis nematic Bose-Einstein condensates”.

Topological defects are classified by the order parameter space of the considered system in the ground state.

Although the global or external structure of a defect is determined typically by the homotopy theory, the internal structure in the “core” of defects can be nontrivial by some sort of energy hierarchy in the presence of a characteristic length scale in addition to the healing length of the bulk order parameter.

This aspect of topological defects has not been well known but is important since the internal structure can change static and dynamic properties of defects drastically.

Here, we show an important, timely example of such systems, the polar phase of spin-1 Bose-Einstein condensates with easy-axis nematic order, and discuss mainly on our recent contiributions [1-4].

[1] Hiromitsu Takeuchi, Phys. Rev. A 104, 013316 (2021)

[2] Hiromitsu Takeuchi, Phys. Rev. Lett. 126, 195302 (2021)

[3] I-Kang Liu, et.al., Phys. Rev. Research 2, 033506 (2020)

[4] Seji Kang, et.al., Phys. Rev. Lett. 122, 095301 (2019)