  We identify a novel regime of soliton-plasma interactions in which
high-intensity ultrashort pulses of intermediate soliton order undergo coherent
plasma-induced fission. Experimental results obtained in gas-filled hollow-core
photonic crystal fibers are supported by rigorous numerical simulations. The
cumulative blueshift of higher-order input solitons with ionizing intensities
results in pulse splitting before the ultimate self-compression point, leading
to the generation of robust pulse pairs with PHz bandwidths. The novel dynamics
closes the gap between plasma-induced adiabatic soliton compression and
modulational instability.
