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Mixed-valence state in the dilute-impurity regime of La-substituted SmB6

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Michiardi,  M.
Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Zonno, M., Michiardi, M., Boschini, F., Levy, G., Volckaert, K., Curcio, D., et al. (2024). Mixed-valence state in the dilute-impurity regime of La-substituted SmB6. Nature Communications, 15(1): 7621, pp. 1-7. doi:10.1038/s41467-024-51569-2.


Cite as: https://hdl.handle.net/21.11116/0000-000F-D3EE-7
Abstract
Homogeneous mixed-valence (MV) behaviour is one of the most intriguing phenomena of f-electron systems. Despite extensive efforts, a fundamental aspect which remains unsettled is the experimental determination of the limiting cases for which MV emerges. Here we address this question for SmB6, a prototypical MV system characterized by two nearly-degenerate Sm2+ and Sm3+ configurations. By combining angle-resolved photoemission spectroscopy (ARPES) and x-ray absorption spectroscopy (XAS), we track the evolution of the mean Sm valence, vSm, in the SmxLa1−xB6 series. Upon substitution of Sm ions with trivalent La, we observe a linear decrease of valence fluctuations to an almost complete suppression at x = 0.2, with vSm ~ 2; surprisingly, by further reducing x, a re-entrant increase of vSm develops, approaching the value of vimp ~ 2.35 in the dilute-impurity limit. Such behaviour departs from a monotonic evolution of vSm across the whole series, as well as from the expectation of its convergence to an integer value for x → 0. Our ARPES and XAS results, complemented by a phenomenological model, demonstrate an unconventional evolution of the MV character in the SmxLa1−xB6 series, paving the way to further theoretical and experimental considerations on the concept of MV itself, and its influence on the macroscopic properties of rare-earth compounds in the dilute-to-intermediate impurity regime. © The Author(s) 2024.