  Nontrivial topology in condensed matter systems enriches quantum states of
matter, to go beyond either the classification into metals and insulators in
terms of conventional band theory or that of symmetry broken phases by Landau's
order parameter framework. So far, focus has been on weakly interacting
systems, and little is known about the limit of strong electron correlations.
Heavy fermion systems are a highly versatile platform to explore this regime.
Here we report the discovery of a giant spontaneous Hall effect in the Kondo
semimetal Ce3Bi4Pd3 that is noncentrosymmetric but preserves time reversal
symmetry. We attribute this finding to Weyl nodes - singularities of the Berry
curvature - that emerge in the immediate vicinity of the Fermi level due to the
Kondo interaction. We stress that this phenomenon is distinct from the
previously detected anomalous Hall effect in materials with broken time
reversal symmetry; instead, it manifests an extreme topological response that
requires a beyond-perturbation-theory description of the previously proposed
nonlinear Hall effect. The large magnitude of the effect in even tiny electric
and zero magnetic fields, as well as its robust bulk nature may aid the
exploitation in topological quantum devices.
