Anisotropic superfluidity in a dipolar Bose gas

TL;DR

This paper investigates the anisotropic superfluid behavior of a dipolar Bose-Einstein condensate in a quasi-two-dimensional setup, revealing direction-dependent critical velocities and vortex formation due to anisotropic interactions and roton modes.

Contribution

It introduces the study of anisotropic superfluidity in a dipolar BEC with tilted polarization, highlighting the impact on quasiparticle dispersion and critical velocities.

Findings

Critical velocities vary with probe direction.

Anisotropic dispersion due to dipole tilt.

Vortex-antivortex pairs form at different thresholds.

Abstract

We study the superfluid character of a dipolar Bose-Einstein condensate (DBEC) in a quasi-two dimensional (q2D) geometry. In particular, we allow for the dipole polarization to have some non-zero projection into the plane of the condensate so that the effective interaction is anisotropic in this plane, yielding an anisotropic dispersion for propagation of quasiparticles. By performing direct numerical simulations of a probe moving through the DBEC, we observe the sudden onset of drag or creation of vortex-antivortex pairs at critical velocities that depend strongly on the direction of the probe's motion. This anisotropy emerges because of the anisotropic manifestation of a roton-like mode in the system.