We have measured the thermal conductivity of the Kondo insulator SmB₆ at temperatures down to 70 mK, in a magnetic field up to 15 T. Several samples grown by floating-zone method were investigated [1] as well as flux grown samples. We observe a large enhancement of thermal conductivity with field, but no residual linear term at T = 0 in any field. We discuss two possible mechanisms for the field dependence:
1) heat transport by phonons scattered by low-energy magnetic excitations;
2) heat transport by magnetic excitations.

Furthermore, the field dependence is anisotropic depending on whether the magnetic field is applied parallel or perpendicular to the heat current. This anisotropy varies significantly from sample to sample, indicating that magnetic impurities may play an important role in the heat transport of SmB₆.

We compare our results to a recently published study [2] and discuss how to reconcile current discrepancies in experimental observations on SmB₆.

[1] M-E. Boulanger et al., arxiv: 1709.10456

[2] M. Hartstein et al., Nat. Phys. (2017)