Birth and breakdown of breathing and rotobreathing cyclops states in Kuramoto networks with higher-mode coupling

Cluster synchronization states often serve as organizing centers for collective dynamics, but their destabilization can open unexpected routes to both coherent and incoherent behaviors. We study such transitions for cyclops states in globally coupled networks of identical Kuramoto-Sakaguchi rotators with inertia and two-harmonic coupling. Stationary cyclops states consist of two coherent clusters and a solitary oscillator that maintains fixed phase differences with the clusters. Using Floquet analysis and numerical continuation of periodic orbits, we trace bifurcation routes for the birth and breakdown of breathing and rotobreathing cyclops states with nonstationary intercluster phase differences. Breathing cyclops states, born from their stationary counterparts, correspond to bounded oscillations of the intercluster phases. They lose stability via period-doubling bifurcations, which produce phase-split cyclops states whose intercluster motion repeats only after two cycles of the parent breather, or via cluster-destruction bifurcations. Rotobreathing cyclops states, in which the intercluster phase differences undergo full rotations, are not, in general, merely breathing cyclops states whose oscillation amplitude has grown sufficiently large; rather, they predominantly arise through global bifurcations involving heteroclinic-contour-like structures formed by saddle cluster states. We further show that these states have wide basins of attraction, persist in large odd-sized networks, and contrast sharply with even-sized networks, where stationary multi-cluster states dominate. These results identify higher-mode coupling and solitary-oscillator-mediated rotations as generic mechanisms for organizing complex cluster motion in phase oscillator networks.