Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2006-05-31
Physical Review B 74 (2006) 035114
Physics
Condensed Matter
Strongly Correlated Electrons
Submitted to Phys. Rev; B (14 pages, 13 figures, 2 tables)
Scientific paper
10.1103/PhysRevB.74.035114
Mixed-valence phenomena occurring in the "black" (B) and "gold" (G) phases of Sm1-x Yx S have been studied by x-ray diffraction, x-ray absorption spectroscopy, and inelastic neutron scattering. Lattice-constant and phonon-dispersion results confirm that the valence instability occurs already inside the B phase. On the other hand, pronounced temperature anomalies in the thermal expansion \alpha(T), as well as in the Sm mean-square displacements denote the onset of the B-G transition for the compositions x = 0.33 and 0.45. It is argued that these anomalies primarily denote an effect of electron-phonon coupling. The magnetic spectral response, measured on both powder and single crystals, is dominated by the Sm2+ spin-orbit component close to 36 meV. A strongly overdamped Sm3+ contribution appears only for x >= 0.33 near room-temperature. The quasielastic signal is strongly suppressed below 70 K, reflecting the formation of the singlet mixed-valence ground state. Quite remarkably, the signal around 36 meV is found, from the single-crystal spectra, to arise from two distinct, dispersive, interacting branches. The lower peak, confirmed to exist from x = 0.17 to x = 0.33 at least, is tentatively ascribed to an excitation specific to the mixed-valence regime, reminiscent of the "exciton" peak reported previously for SmB6 .
Alekseev P. A.
Bewley R. I.
Chernikov R. V.
Golubkov A. V.
Klementiev K. V.
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