Proposed measurement of spatial correlations at the Berezinski-Kosterlitz- Thouless transition of superconducting thin films

The Berezinski-Kosterlitz-Thouless transition is a unique two-dimensional phase transition, separating two phases with exponentially and power-law decaying correlations, respectively. In disordered systems, these correlations propagate along favorable paths, with the transition marking the point where global coherence is lost. Here we propose an experimental method to probe locally these particular paths in superconducting thin films, which exhibit this transition, and demonstrate theoretically that close to the transition the coherence propagates along a ramified network, reminiscent of a percolation transition. We suggest and calculate experimentally accessible quantities that can shed light on the spatial correlations in the system as it approaches the critical point. This approach can be applicable to a variety of phase transitions in disordered systems.