  Long known to have thermodynamic properties at odds with its insulating
electrical transport, SmB6 has been the subject of great debate as it is
unclear whether its unusual properties are related to the bulk or novel
metallic surface states. We have observed a bulk moment-screening effect in
nominally pure and Gd-doped SmB6 via heat capacity, magnetization, and
resistivity measurements, and show this new Kondo-impurity like effect provides
an unexpected but intuitive explanation for metal-like phenomena stemming from
the strongly interacting host system. This affords a coherent understanding for
decades of mysteries in strongly-correlated insulators, reveals the expanded
utility of techniques previously only utilized for metals, and presents the
novel effect of even highly-dilute impurities in strongly correlated
insulators.
