Entropy- and Flow- Induced Superfluid States

Normally the role of phase fluctuations in superfluids and superconductors is to drive a phase transition to the normal state. This happens due to proliferation of topologically nontrivial phase fluctuations in the form of vortices. Here we discuss a class of systems where, by contrast, nontopological phase fluctuations can produce superfluidity. Here we understand superfluidity as a phenomenon that does not necessarily arises from a broken $U(1)$ symmetry, but can be associated with a certain class of (approximate or exact) degeneracies of the systems energy landscape giving raise to a $U(1)$-like phase.