Crystalline electric field and Kondo effect in SmOs₄Sb₁₂

Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs₄Sb₁₂ has the Γ₆₇ quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the Γ₆₇ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic response below ≈20 T cannot be explained using the localized 4f-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures. (author)