Gap formation and in-gap bound states are investigated in ${\mathrm{SmB}}_6$ using Raman scattering. Below 70 K, we observe an abrupt suppression of electronic scattering below ∼290 ${\mathrm{cm}}^{\mathrm{-}1}$ that is not consistent with the predicted temperature dependence of a hybridization gap. We also find that gap formation in ${\mathrm{SmB}}_6$ is associated with the appearance of a sharp ${\mathit{E}}_{\mathit{g}}$(${\mathrm{\Gamma }}_3^{+}$) symmetry 130-${\mathrm{cm}}^{\mathrm{-}1}$ excitation. We discuss several possible interpretations of this excitation, including a ${\mathrm{\Gamma }}_7$-${\mathrm{\Gamma }}_8$ crystal-field transition and a transition between bound 4${\mathit{f}}^5$5d configurations.

• Received 5 July 1995

DOI:https://doi.org/10.1103/PhysRevB.52.R14308