Theory of the vortex-clustering transition in a confined two-dimensional quantum fluid

Understand

Clustering of like-sign vortices in a planar bounded domain is known to occur at negative temperature, a phenomenon that Onsager demonstrated to be a consequence of bounded phase space.

• In a confined superfluid, quantized vortices can support such an ordered phase, provided they evolve as an almost isolated subsystem containing sufficient energy.
• A detailed theoretical understanding of the statistical mechanics of such states thus requires a microcanonical approach.
• Here we develop an analytical theory of the vortex clustering transition in a neutral system of quantum vortices confined to a two-dimensional disk geometry, within the microcanonical ensemble.