Samarium hexaboride (SmB₆), a well-known Kondo insulator in which the insulating behavior of the bulk arises from strong electron correlations, has recently attracted great attention owing to its possible topological nature. Although there is strong evidence for this, corroborative spectroscopic evidence was lacking; unlike in the weakly correlated counterparts, e.g., Bi₂Se₃. Our planar tunneling spectroscopy results reveal the linear density of states (DOS) as expected for Dirac cones. The energy and temperature dependence indicate that the topological surface states are not protected above a certain temperature and energy range, and we invoke an inelastic tunneling model involving spin excitons [2.3] that accounts for the observed behavior.

[1] W.K. Park et al., “Topological surface states interacting with bulk excitons in the Kondo insulator SmB₆ revealed via planar tunneling spectroscopy” PNAS 113, 6599 (2016).

[2] W.T. Fuhrman et al., “Interaction driven subgap spin exciton in the Kondo insulator SmB₆” Phys. Rev. Lett. 114, 036401 (2015).

[3] G.A. Kapilevich et al. “Incomplete protection of the surface Weyl cones of the Kondo insulator SmB6: Spin exciton scattering” Phys. Rev. B 92, 085133 (2015).