prediction [15e18] that Kondo insulators can be topological insulators.
Topological insulators, which have been the subject of
intense theoretical and experimental investigation over the last
years, are insulating in the bulk but have in their gap metallic
surface states. The TKI approach for SmB6 has been recently supported
by a number of various experimental studies (see e.g.
[19e21]). Specifically in [20], where transport properties were
investigated on a sample with specialized geometry and eight
coplanar electrical contacts (four on each side of the sample), below
4 K a crossover from bulk to surface conduction with a fully insulating
bulk was observed.
Very recently a model based on valence-fluctuation induced
hopping was proposed as a new possibility to explain the unusual
metallic-like conduction of SmB6 and of other Kondo insulators at
lowest temperatures [22].
In this paper we present results of detailed electrical resistivity
measurements performed on five various SmB6 single crystals with
the aim to contribute to determination of the origin of charge
transport, particularly in the lowest temperature range. Results
received on some of these samples have been already published
[23], however, in this paper they are used to compare them with the
latest results and to undertake the corresponding analysis.