Surface and bulk components of electrical conductivity in the (presumably special topological) Kondo insulator SmB6 at lowest temperatures

TL;DR

This study investigates the electrical conductivity of SmB6 at very low temperatures, revealing that residual conductivity arises from both surface states typical of topological insulators and a correlated bulk ground state.

Contribution

It provides evidence that SmB6 exhibits both surface and bulk conduction contributions, suggesting a novel type of topological insulator with a correlated bulk in addition to surface states.

Findings

Residual conductivity below 4 K is metallic-like.

Both surface states and bulk correlated states contribute to conductivity.

SmB6 may represent a new topological insulator with in-gap bulk conduction.

Abstract

Samarium hexaboride (SmB6) has recently been considered to be a topological Kondo insulator (TKI), the first strongly correlated electron system to exhibit topological surface conduction states. In this contribution, results of electrical resistivity measurements between 80 K and 0.08 K of various SmB6 single crystalline samples are presented, analyzed and discussed. The received results imply that the residual conductivity of SmB6 below about 4 K is of non-activated (metallic-like) nature. It is shown that this metallic-like behavior can be attributed both to surface (2D) conduction states, as may be expected in case of a topological insulator, as well as to the highly correlated many-body (3D) bulk ground state which is formed within the gap of this compound. From this it follows that in SmB6, where surface conductivity states are clearly present, there is in parallel also a bulk contribution to residual electrical conductivity originating from the strongly correlated electron system with valence fluctuations. This raises the question whether SmB6 does not form a new / special type of topological insulator in which in the energy gap besides the surface conduction states, there is also a conducting narrow in-gap band originating from the bulk strongly correlated electron system.