  We investigate the quantum recoil force acting on an excited atom close to
the surface of a nonreciprocal photonic topological insulator (PTI). The main
atomic emission channel is the unidirectional surface-plasmon propagating at
the PTI-vacuum interface, and we show that it enables a spontaneous lateral
recoil force that scales at short distance as $1/d^4$, where $d$ is the
atom-PTI separation. Remarkably, the sign of the recoil force is polarization
and orientation-independent, and it occurs in a translation-invariant
homogeneous system in thermal equilibrium. Surprisingly, the recoil force
persists for very small values of the gyration pseudovector, which, for a
biased plasma, corresponds to very low cyclotron frequencies. The ultra-strong
recoil force is rooted on the quasi-hyperbolic dispersion of the
surface-plasmons. We consider both an initially excited atom and a continuous
pump scenario, the latter giving rise to a continuous lateral force whose
direction can be changed at will by simply varying the orientation of the
biasing magnetic field. Our predictions may be tested in experiments with cold
Rydberg atoms and superconducting qubits.
