Borromean Supercounterfluids

While the properties of standard (single-component) superfluids are well understood, principal differences arise in a special type of multi-component systems—the so-called Borromean supercounterfluids—in which (i) supertransport is possible only in the counterflow regime and (ii) there are three or more counterflowing components. Borromean supercounterfluids feature correlation and topological properties distinguishing them from their single- and two-component counterparts. Especially interesting is the component-symmetric case characterized by a distinctively different universality class of the supercounterfluid-to-normal phase transition. Using the recently introduced concept of compact-gauge invariance as the guiding principle, we develop the finite-temperature description of Borromean supercounterfluids in terms of an asymptotically exact long-wave effective action. We formulate and study Borromean XY and loop statistical models, capturing the universal long-range properties and allowing us to perform efficient worm algorithm simulations. Numeric results demonstrate perfect agreement with analytic predictions. Particularly instructive is the two-dimensional case, where Borromean nature of the system is strongly manifested while allowing for an asymptotically exact analytic description.