# Landau's criterion for an anisotropic Bose-Einstein condensate

## TL;DR

This paper investigates Landau's criterion for anisotropic superfluidity in Bose-Einstein condensates with dipole interactions or spin-orbit coupling, revealing how anisotropy affects critical velocities and dissipation.

## Contribution

It introduces a detailed analysis of Landau's criterion in anisotropic BECs with dipole and spin-orbit interactions, providing explicit calculations of energy dissipation and critical velocities.

## Key findings

- Critical velocity is generally smaller than sound velocity in the moving direction.
- Dissipation rate is explicitly calculated beyond the critical velocity.
- Raman coupling suppresses dissipationless motion in spin-orbit coupled BECs.

## Abstract

In this work, we discuss the Landau's criterion for anisotropic superfluidity. To this end, we consider a point-like impurity moving in a uniform Bose-Einstein condensate with either interparticle dipole-dipole interaction or Raman induced spin-orbit coupling. In both cases, we find that the Landau critical velocity $v_{\rm c}$ is generally smaller than the sound velocity in the moving direction. Beyond $v_{\rm c}$, the energy dissipation rate is explicitly calculated via a perturbation approach. In the plane-wave phase of a spin-orbit coupled Bose gas, the dissipationless motion is suppressed by the Raman coupling even in the direction orthogonal to the recoil momentum. Our predictions can be tested in the experiments with ultracold atoms.