Stable vortex solitons in a ring-shaped partially-PT-symmetric potential

We address the existence and stability of vortex solitons in a ring-shaped partially-parity-time (pPT) configuration. In sharp contrast to the reported nonlinear modes in PT- or pPT-symmetric systems, stable vortex solitons with different topological charges can be supported by the proposed pPT potential, despite the system always being beyond the symmetry-breaking point. Vortex solitons are characterized by the number of phase singularities which equals the corresponding topological charge. At higher power, unstable higher-charged vortices degenerate into stable vortices with lower charges. Robust nonlinear vortices can be easily excited by an input Gaussian beam. Our results provide, to the best of our knowledge, the first example of stable solitons in a symmetry-breaking system.