Drag force and superfluidity in the supersolid stripe phase of a spin-orbit-coupled Bose-Einstein condensate

TL;DR

This paper investigates the superfluid properties of the supersolid stripe phase in a spin-orbit-coupled Bose-Einstein condensate, revealing unique drag force behaviors and energy dissipation characteristics due to the phase's gapless spectrum and spin-orbit effects.

Contribution

It provides a detailed analysis of superfluidity and drag force in the supersolid stripe phase, highlighting the effects of spin-orbit coupling on dissipation and impurity motion.

Findings

Landau critical velocity vanishes unless motion is parallel to stripes.

Drag force can have a perpendicular component due to spin-orbit coupling.

Energy dissipation is negligible for slow impurities over several seconds.

Abstract

The phase diagram of a spin-orbit-coupled two-component Bose gas includes a supersolid stripe phase, which is featuring density modulations along the direction of the spin-orbit coupling. This phase has been recently found experimentally [J.~Li \textit{et al.}, Nature (London) \textbf{543}, 91 (2017)]. In the present work we characterize the superfluid behavior of the stripe phase by calculating the drag force acting on a moving impurity. Because of the gapless band structure of the excitation spectrum, the Landau critical velocity vanishes if the motion is not strictly parallel to the stripes, and energy dissipation takes place at any speed. Moreover, due to the spin-orbit coupling, the drag force can develop a component perpendicular to the velocity of the impurity. Finally, by estimating the time over which the energy dissipation occurs, we find that for slow impurities the effects of friction are negligible on a time scale up to several seconds, which is comparable with the duration of a typical experiment.