Thermal waves, criticality, and self-organization in excitable media

Thermal waves are noise-sustained excitation patterns in excitable media coupled to a thermal environment. The coherence and spatiotemporal organization of thermal waves is quantitatively analyzed by utilizing the novel method of coherent space-time clusters. As our main result we find for strongly correlated thermal fluctuations a power-law scaling of the cluster-size distribution with a universal exponent-the fingerprint of self-organized criticality.