  Strongly correlated Kondo insulator SmB6 is known for its peculiar low
temperature residual conduction, which has recently been demonstrated to arise
from a robust metallic surface state, as predicted by the theory of topological
Kondo insulator (TKI). Photoemission, quantum oscillation and magnetic doping
experiments have provided evidence for the Dirac-like dispersion and
topological protection. Questions arise as whether signatures of spin-momentum
locking and electron interaction could be resolved in transport measurements.
Here we report metallic conduction of surface state down to mK temperatures
with saturation behaviors suggestive of Kondo effect. We observe in the surface
state the weak-antilocalization (WAL) effect that is in agreement with a
spin-momentum locked metallic surface. At larger perpendicular magnetic fields,
the surface state exhibits an unusual linear magnetoresistance similar to those
found in Bi-based topological insulators and in graphene. (Correspondence to:
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