Low-energy excitations of the correlation-gap insulator:ffA light-scattering study

We present the results of Raman scattering studies of single-crystal SmB₆ for temperatures down to 4 K and in magnetic fields up to 8 T. At temperatures below T*∼50 K the electronic Raman continuum exhibits an abrupt redistribution of scattering intensity around a temperature-independent ("isobestic") energy, Δ_c ∼290cm^-1, reflecting the opening of a pseudogap which is larger than previously suggested by transport measurements. Additionally, the Raman response exhibits at least four well-defined excitations within the gap below T*. The field dependencies of some of these in-gap states are consistent with the expected g factor (g_eff=2/7) for the Sm³⁺ Γ₈ level, suggesting that these gap edge states are crystal-electric-field excitations of the Sm³⁺ ion split by magnetoelastic coupling.