We show that the motion of spin-polarized impurity (ferron) in ultracold atomic gas is characterized by a certain critical velocity which can be traced back to the amount of spin imbalance inside the impurity. We have calculated the effective mass of ferron in two dimensions. We show that the effective mass scales with the surface of the ferron. We discuss the impact of these findings; in particular, we demonstrate that ferrons become unstable in the vicinity of a vortex.

• Received 10 February 2021
• Revised 24 June 2021
• Accepted 26 July 2021

DOI:https://doi.org/10.1103/PhysRevA.104.033304