Creation of excitations from a uniform impurity motion in the condensate

TL;DR

This paper studies how excitations are generated in a homogeneous Bose-Einstein condensate by a moving impurity, revealing finite excitations below the critical velocity and analyzing their scaling behavior.

Contribution

It introduces a simple dynamical model showing excitations can occur below Landau's critical velocity and explores the critical behavior across the speed of sound.

Findings

Finite excitations can be created below the critical velocity.

The number of excitations scales differently over time depending on the impurity speed.

Landau's critical velocity validity is supported within the model.

Abstract

We investigate a phenomenon of creation of excitations in the homogenous Bose-Einstein condensate due to an impurity moving with a constant velocity. A simple model is considered to take into account dynamical effects due to motions of the impurity. Based on this model, we show that there can be a finite amount of excitations created even if velocity of the impurity is below Landau's critical velocity. We also show that the total number of excitations scales differently for large time across the speed of sound. Thus, our result dictates the critical behavior across Landau's one and validates Landau's institution to the problem. We discuss how Landau's critical velocity emerges and its validity within our model.