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

M. Zonno (), M. Michiardi, F. Boschini, G. Levy, K. Volckaert, D. Curcio, M. Bianchi, P. F. S. Rosa, Z. Fisk, Ph. Hofmann, I. S. Elfimov, R. J. Green, G. A. Sawatzky and A. Damascelli ()
Additional contact information
M. Zonno: University of British Columbia
M. Michiardi: University of British Columbia
F. Boschini: University of British Columbia
G. Levy: University of British Columbia
K. Volckaert: Aarhus University
D. Curcio: Aarhus University
M. Bianchi: Aarhus University
P. F. S. Rosa: Los Alamos National Laboratory
Z. Fisk: University of California
Ph. Hofmann: Aarhus University
I. S. Elfimov: University of British Columbia
R. J. Green: University of British Columbia
G. A. Sawatzky: University of British Columbia
A. Damascelli: University of British Columbia

Nature Communications, 2024, vol. 15, issue 1, 1-7

Abstract: 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.

Date: 2024
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DOI: 10.1038/s41467-024-51569-2

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