Vortices, antivortices and superfluid shells separating Mott-insulating regions

TL;DR

This paper investigates the emergence of superfluid shells and vortex-antivortex phenomena in confined bosonic systems with Mott-insulating regions, revealing complex excitation spectra and phase transitions.

Contribution

It introduces a detailed analysis of superfluid shells between Mott insulators, including their excitation spectra and vortex dynamics, extending understanding beyond traditional Gross-Pitaevskii models.

Findings

Superfluid shells exhibit low energy sound modes with spatially varying velocities.

Vortex-antivortex pairs are analyzed within the superfluid shells and rings.

The excitation spectra differ significantly from standard models near Mott boundaries.

Abstract

Atomic or molecular bosons in harmonically confined optical lattices exhibit a wedding cake structure consisting of insulating (Mott) shells. It is shown that superfluid regions emerge between Mott shells as a result of fluctuations due to finite hopping. It is found that the order parameter equation in the superfluid region is not of the Gross-Pitaeviskii type except near the insulator to superfluid boundaries. The excitation spectra in the Mott and superfluid regions are obtained, and it is shown that the superfluid shells posses low energy sound modes with spatially dependent sound velocity described by a local index of refraction directly related to the local superfluid density. Lastly, the Berezinskii-Kosterlitz-Thouless transition and vortex-antivortex pairs are discussed in thin (wide) superfluid shells (rings) limited by three (two) dimensional Mott regions.