Department Colloquium | Correlated Topological Materials

In Kondo insulators, strong correlation and band hybridization lead to a diverging resistance at low temperature. The resistance divergence ends at about 3 Kelvin, a behavior due to the surface conductance. Quantum oscillations were observed in magnetization, but not in electrical resistivity. This difference raised many speculations if a charge-neutral Fermi Surface exists in insulators and these fermions interact only with the magnetic field, not with electric fields. We solved the problem by resolving the Landau Level quantization and Fermi Surface topology in the electrical resistivity a Kondo insulator Ytterbium Dodecaboride (YbB12). The temperature dependence of the oscillation amplitude follows the conventional Fermi liquid theory of metals with a large effective mass. The result suggests that the observed Fermi surface originates from the charged particles. Our finding reveals a mysterious dual nature of the ground state in Kondo insulator YbB12: it is both a charge insulator and a strongly correlated topological metal.