  Recent experiments on Kondo insulator SmB6 have revealed bulk excitations
that could be Fermions without charge. This would lead to a residual linear
term in the thermal conductivity that was not observed universally in
experiments. To solve this mystery, we introduce a novel symmetric geometry for
performing thermal transport measurements under strains.
Magnetic-field-independent residual linear terms were found in flux-grown SmB6
at nominal zero strain, and they grew under a tensile strain, which is known to
modify Sm valence. A small growth-dependent difference in the Sm valence might
explain the observed discrepancies. We discuss the constraints on the theories
of bulk excitations in SmB6.
