Vortex Lattice Inhomogeneity in Spatially Inhomogeneous Superfluids

TL;DR

This paper investigates vortex distribution in inhomogeneous superfluids, revealing that vortices tend to distribute uniformly despite density variations, with implications for superfluid flow and angular momentum transfer.

Contribution

It demonstrates that vortex arrangements in inhomogeneous superfluids are nearly uniform and explains the underlying physics of this phenomenon.

Findings

Vortex density remains nearly uniform despite superfluid inhomogeneity.

Inhomogeneity diminishes at rapid rotation, favoring vortex density at the center.

Superfluid velocity deviates from rigid-body rotation, showing radial shear.

Abstract

A trapped degenerate Bose gas exhibits superfluidity with spatially nonuniform superfluid density. We show that the vortex distribution in such a highly inhomogeneous rotating superfluid is nevertheless nearly uniform. The inhomogeneity in vortex density, which diminishes in the rapid-rotation limit, is driven by the discrete way vortices impart angular momentum to the superfluid. This effect favors highest vortex density in regions where the superfluid density is most uniform (e.g., the center of a harmonically trapped gas). A striking consequence of this is that the boson velocity deviates from a rigid-body form exhibiting a radial-shear flow past the vortex lattice.