  The interplay of Kondo screening and magnetic ordering in strongly correlated
materials containing local moments is a subtle problem.[1] Usually the number
of conduction electrons matches or exceeds the number of moments, and a
Kondo-screened heavy Fermi liquid develops at low temperatures.[2] Changing the
pressure, magnetic field, or chemical doping can displace this heavy Fermi
liquid in favor of a magnetically ordered state.[3,4] Here we report the
discovery of a version of such a `Kondo lattice' material, YbIr$_3$Si$_7$, in
which the number of free charge carriers is much less than the number of local
moments. This leads to `Kondo exhaustion':[5] the electrical conductivity tends
to zero at low temperatures as all the free carriers are consumed in the
formation of Kondo singlets. This effect coexists with antiferromagnetic
long-range order, with a N\'eel temperature $T\rm_N = 4.1\,{\rm K}$.
Furthermore, the material shows conductive surface states with potential
topological nature, and thus presents an exciting topic for future
investigations.
