Critical velocity of a mobile impurity in one-dimensional quantum liquids

Michael Schecter, Alex Kamenev, Dimitri Gangardt, Austen Lamacraft 2012. Physical Review Letters

Abstract

We study the notion of superfluid critical velocity in one spatial dimension. It is shown that for heavy impurities with mass \(M\) exceeding a critical mass \(M_c\), the dispersion develops periodic metastable branches resulting in dramatic changes of dynamics in the presence of an external driving force. In contrast to smooth Bloch Oscillations for \(M<M_c\), a heavy impurity climbs metastable branches until it reaches a branch termination point or undergoes a random tunneling event, both leading to an abrupt change in velocity and an energy loss. This is predicted to lead to a non-analytic dependence of the impurity drift velocity on small forces.