Entropic-ordered superfluid

We present a minimal classical lattice model of superfluidity at arbitrarily high temperatures, using a modified three-dimensional XY model with ``soft" rotors. The global U(1) symmetry is spontaneously broken above a positive critical temperature due to entropic order. We study hydrodynamics in this high-temperature regime and verify consistency with the fluctuation-dissipation theorem, explaining how the large noise variance at very high temperatures is not sufficient to destroy superfluidity or the long lifetime of Goldstone modes.