Drag effect and topological complexes in strongly interacting two-component lattice superfluids

TL;DR

This paper investigates the mutual drag phenomena in strongly interacting two-component lattice superfluids, revealing novel topological excitations and fractional vortex states, with implications for optical lattice experiments.

Contribution

It introduces the concept of topological complexes and fractional vortices arising from competing drag mechanisms in two-component superfluids in optical lattices.

Findings

Identification of vacancy-assisted and quasi-molecular drag mechanisms.

Prediction of fractional circulation quanta in topological excitations.

Demonstration of detection methods via absorptive imaging.

Abstract

The mutual drag in strongly interacting two-component superfluids in optical lattices is discussed. Two competing drag mechanisms are the vacancy-assisted motion and proximity to the quasi-molecular state, in which an integer number $q$ of atoms (or holes) of one component might be bound to one atom (or hole) of the other component. Then the lowest energy topological excitation (vortex or persistent current) becomes a composite object consisting of $q$ circulation quanta of one component and one circulation of the other. In the SQUID-type geometry, the value of $q$ can become fractional. These topological complexes can be detected by absorptive imaging. We present both the mean field and Monte Carlo results. The drag effects in optical lattices are drastically different from the Galilean invariant Andreev-Bashkin effect in liquid helium.