Fermi Surfaces in Kondo Insulators

We report experimental signatures signifying the existence of bulk Fermi surfaces in the Kondo insulator family and compare these with theoretical models. We have observed quantum oscillations, traditionally considered a hallmark of Fermi liquids, in magnetization in the Kondo insulator SmB6 [Hartstein et al., nphys4295]. The quantum oscillations, taken together with measured finite specific heat coefficient at low temperatures, finite quantum oscillatory entropy, and magnetic field enhancement of thermal conductivity, suggest the existence of bulk Fermi surfaces that originate from novel quasiparticles that couple to magnetic fields but not DC electric fields. Since our experimental observation, a number of innovative theories have been proposed to explain how a Fermi surface could arise in charge gapped Kondo insulators. Here, we explore experimental signatures in light of these theoretical proposals.