Bulk Fermi surface of charge-neutral excitations in SmB$_{\mathrm{6}}$ or not: A heat-transport study

Recently, there have been increasingly hot debates on whether a bulk Fermi surface of charge-neutral excitations exists in the topological Kondo insulator SmB$_{\mathrm{6}}$. To unambiguously resolve this issue, we perform the low-temperature thermal conductivity measurements of a high-quality SmB$_{\mathrm{6}}$ single crystal down to 0.1 K and up to 14.5 T. Our experiments show that the residual linear term of thermal conductivity at the zero field is \textit{zero}, within the experimental accuracy. Furthermore, the thermal conductivity is insensitive to the magnetic field up to 14.5 T. These results demonstrate the absence of fermionic charge-neutral excitations in bulk SmB$_{\mathrm{6}}$, such as scalar Majorana fermions or spinons and, thus, exclude the existence of a bulk Fermi surface suggested by a recent quantum oscillation study of SmB$_{\mathrm{6}}$. This puts a strong constraint on the explanation of the quantum oscillations observed in SmB$_{\mathrm{6}}$. [1] Y. Xu, S. Cui, J. K. Dong, D. Zhao, T. Wu, X. H. Chen, Kai Sun, Hong Yao, and S. Y. Li, Phys. Rev. Lett. 116, 246403 (2016).