Low-temperature surface conduction in the Kondo insulator SmB6

Abstract

We study the transport properties of the Kondo insulator SmB 6 with a specialized configuration designed to distinguish bulk-dominated conduction from surface-dominated conduction. We find that as the material is cooled below 4 K, it exhibits a crossover from bulk to surface conduction with a fully insulating bulk. We take the robustness and magnitude of the surface conductivity, as is manifest in the literature of SmB 6 , to be strong evidence for the topological insulator metallic surface states recently predicted for this material.

Crossover of Magnetoresistance from Fourfold to Twofold Symmetry in SmB6 Single Crystal, a Topological Kondo Insulator

“…In such a range, it is widely believed that the Kondo insulator SmB 6 has an insulating bulk with a Kondo gap and 2D metallic surface states [21][22][23][24]. Therefore, the transition of MR from C 4 to C 2 symmetry indicates a crossover from 3D metallic bulk states to 2D metallic surface states with an insulating bulk.…”

“…The most puzzling issue is the lack of divergence in the resistivity at low temperatures, which has always been attributed to in-gap states [13][14][15][16]. Recently, there have been theoretical and experimental demonstrations that such in-gap states might be topological surface states [17][18][19][20][21][22][23][24].…”

Effects of spin excitons on the surface states of SmB6 : A photoemission study

“…High-quality SmB6 crystals were grown using aluminum flux method in a continuous Ar purged vertical high temperature tube furnace [9]. High-resolution valence-band photoemission measurements were carried out in the normal emission geometry using linearly p-polarized light with photon energy of 35 eV at the 1 3 end-station of the BESSY II storage ring of the Helmholtz-Zentrum Berlin.…”

“…Thus, the bulk properties are characterized by a thermal activation in the resistivity and specific heat with an activation energy of about 4 meV [4,5,6]. However, at temperatures of the order of 4 K the resistivity shows a plateau [7,8] indicative of the presence of surface states at the Fermi-energy [9,10,3,11,12]. The material SmB 6 has been the focus of much renewed interest ever since it was proposed that SmB 6 is a topological Kondo Insulator [13,14].…”

Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

“…A condition for a material to become topologically non-trivial is for certain energy bands to invert (other promising examples such as topological Kondo insulators have recently been predicted [8] with experiments in the initial phase [9][10][11][12][13]). Band inversion is most easily achieved in narrow gap semiconductors that are predicted to have non-inverted bands, and by incorporating realistic spin-orbit coupling the energy bands invert [7].…”