Evidence for gap anisotropy in SmB6

Resistivity measurements under uniaxial stress have been performed on the intermediate valence compound SmB₆ for various directions of the crystal. The experimental technique allows us to explore a limited pressure area (basically 0-3 kbar). Nevertheless, the results clearly show an anisotropy; indeed, the effect of the stress in the decrease of the residual resistivity is much higher in the <1 1 1> direction than in the <1 0 0> and the <1 1 0> orientations. This change is witness to the gap anisotropy which must be linked to the theory of excitonic semiconductors.