Cusp solitons mediated by a topological nonlinearity.

Nonlinearity in the Schrödinger equation gives rise to rich phenomena such as soliton formation, modulational instability, and self-organization in diverse physical systems. Motivated by recent advances in engineering nonlinear gauge fields in Bose-Einstein condensates and photonic lattices, we introduce a nonlinear Schrödinger model whose dynamics are dependent on the curvature of the wavefunction intensity and show that this has a direct link to a topological quantity from persistent homology. Our model energetically penalizes or favors the formation of local extrema and we demonstrate through numerical simulations that this topological nonlinearity leads to the emergence of robust, cusp-like soliton structures and supports flat-top beams which do not suffer from conventional modulational instability. These findings suggest that topological nonlinearities could serve as a versatile tool for controlling nonlinear waves in optics and Bose-Einstein condensates.