Over the last few years, researchers from different disciplines have come to realize that many real-world complex systems cannot be appropriately described as single isolated entities, but are the results of many macroscopic sub-systems interacting with one another. As a result of this understanding the model of interdependent networks (i.e. systems where the functionality of a node in one layer depends on the functionality of other nodes in the remaining ones) was developed. In particular, after a seminal article [1], increasing evidence has been collected showing that interdependent networks exhibit unique phenomena resulting in abrupt transitions, for example the famous 2003 Italy blackout.
In our research we focus on the manifestation of the theory of interdependent networks in a real-world physical system. For this purpose, we couple two disordered superconducting networks via a medium that is an electrical insulator but a heat conductor. Because of the disorder each node in the network has its own critical temperature, which allowed us to control the functionality of nodes in the networks. We find that although each individual network undergoes a continuous phase transition, the coupled system undergoes a collective abrupt phase transition. We hope that our results will pave the way to create a new generation of devices and applications.
[1] Sergey V. Buldyrev et al. “Catastrophic cascade of failures in interdependent networks”. Nature 464.7291 (2010), pp. 1025–1028.