Emergence of disconnected clusters in heterogeneous complex systems

TL;DR

This paper reveals that in heterogeneous complex systems, highly correlated sites can be disconnected, challenging traditional views of dense clustering at criticality, with implications for understanding disordered systems and quantum models.

Contribution

It demonstrates that critical dynamics involve mostly one disconnected, highly correlated cluster, using numerical simulations and renormalization group techniques across various dimensions.

Findings

Critical systems feature a dominant disconnected, highly correlated cluster.

Disordered contact process exhibits spatially disconnected but correlated infection patterns.

Results extend to disordered quantum Ising models, showing similar disconnected magnetic domains.

Abstract

Percolation theory dictates an intuitive picture depicting correlated regions in complex systems as densely connected clusters. While this picture might be adequate at small scales and apart from criticality, we show that highly correlated sites in complex systems can be inherently disconnected. This finding indicates a counter-intuitive organization of dynamical correlations, where functional similarity decouples from physical connectivity. We illustrate the phenomena on the example of the Disordered Contact Process (DCP) of infection spreading in heterogeneous systems. We apply numerical simulations and an asymptotically exact renormalization group technique (SDRG) in 1, 2 and 3 dimensional systems as well as in two-dimensional lattices with long-ranged interactions. We conclude that the critical dynamics is well captured by mostly one, highly correlated, but spatially disconnected cluster. Our findings indicate that at criticality the relevant, simultaneously infected sites typically do not directly interact with each other. Due to the similarity of the SDRG equations, our results hold also for the critical behavior of the disordered quantum Ising model, leading to quantum correlated, yet spatially disconnected, magnetic domains.