Date of Original Version
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 a quasimolecular state. In a case of strong drag, the lowest energy topological excitation (vortex or persistent current) can consist of several circulation quanta. In the SQUID-type geometry, the circulation can become fractional. 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.
V. B. Kaurov, A. B. Kuklov, A.E. Meyerovich. Drag Effect and Topological Complexes in Strongly Interacting Two-Component Lattice Superfluids. Phys. Rev. Lett., 95, 090403 (2005). Available at: http://dx.doi.org/10.1103/PhysRevLett.95.090403