MAGNETIC EXCITATION SPECTRUM OF MIXED-VALENCE SMB6 STUDIED BY NEUTRON-SCATTERING ON A SINGLE-CRYSTAL

The paramagnetic response of mixed-valence samarium hexaboride has been studied by inelastic neutron scattering using a low-absorption double-isotope single crystal of (SmB6)-Sm-154-B-11. Measurements were performed for energy transfers 0 less than or equal to h omega less than or equal to 50 meV at temperatures ranging from 2 to 100 K. Two main contributions were observed in the spectra: a broad intermultiplet transition of single-ion type at h omega similar or equal to 36 meV, and a narrow low-energy excitation centred at h omega similar or equal to 14 meV, which is strongly anisotropic and temperature dependent and exhibits a weak but visible dispersion. The latter excitation appears to be an inherent feature of the mixed-valence state due to f-electron hybridization effects, which denotes the formation of a local bound state around the Sm sites.