  Topological insulators, with metallic boundary states protected against
time-reversal-invariant perturbations, are a promising avenue for realizing
exotic quantum states of matter including various excitations of collective
modes predicted in particle physics, such as Majorana fermions and axions.
According to theoretical predictions, a topological insulating state can emerge
from not only a weakly interacting system with strong spin-orbit coupling, but
also in insulators driven by strong electron correlations. The Kondo insulator
compound SmB6 is an ideal candidate for realizing this exotic state of matter,
with hybridization between itinerant conduction electrons and localized
$f$-electrons driving an insulating gap and metallic surface states at low
temperatures. Here we exploit the existence of surface ferromagnetism in SmB6
to investigate the topological nature of metallic surface states by studying
magnetotransport properties at very low temperatures. We find evidence of
one-dimensional surface transport with a quantized conductance value of $e^2/h$
originating from the chiral edge channels of ferromagnetic domain walls,
providing strong evidence that topologically non-trivial surface states exist
in SmB6.
