The random cascading origin of abrupt transitions in interdependent systems

Phase transitions are fundamental features of statistical physics. While the well-studied continuous phase transitions are known to be controlled by external global changes affecting the order parameter, the origin of abrupt transitions is not fully clear. Here we show that abrupt phase transitions may occur due to a unique internal random spatial cascading mechanism, arising from dependency interactions. We experimentally unveil the underlying mechanism of the abrupt transition in interdependent superconducting networks to be governed by a unique metastable state of a long-living resistance cascading plateau. This plateau is characterized by spontaneous cascading events that occur at random locations and last for thousands of seconds, followed by a sudden global phase shift of the system. The plateau time length changes with the system size and distance from criticality, obeying scaling laws with critical exponents. Furthermore, like epidemic spreading, these changes are characterized by a branching factor which equals exactly one at the critical point and deviates from one off criticality. Importantly, the branching factor provides an early warning for the closeness of critical catastrophic cascades yielding system collapse.