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; A Damascelli

doi:10.1038/s41467-024-51569-2

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

Nat Commun. 2024 Sep 2;15(1):7621. doi: 10.1038/s41467-024-51569-2.

Authors

M Zonno^{1

2

3

4}, M Michiardi^{5

6

7}, F Boschini^{6

8}, G Levy^{5

6}, K Volckaert⁹, D Curcio⁹, M Bianchi⁹, P F S Rosa¹⁰, Z Fisk¹¹, Ph Hofmann⁹, I S Elfimov^{5

6}, R J Green^{6

12}, G A Sawatzky^{5

6}, A Damascelli^{13

14}

Affiliations

¹ Department of Physics & Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada. [email protected].
² Quantum Matter Institute, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada. [email protected].
³ Canadian Light Source Inc., Saskatoon, SK, S7N 2V3, Canada. [email protected].
⁴ Synchrotron SOLEIL, Saint-Aubin, 91192, France. [email protected].
⁵ Department of Physics & Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada.
⁶ Quantum Matter Institute, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada.
⁷ Max Planck Institute for Chemical Physics of Solids, Dresden, 01187, Germany.
⁸ Centre Énergie Matériaux Télécommunications Institut National de la Recherche Scientifique, Varennes, QC J3X 1S2, Canada.
⁹ Department of Physics and Astronomy, Interdisciplinary Nanoscience Center, Aarhus University, 8000, Aarhus C, Denmark.
¹⁰ Los Alamos National Laboratory, Los Alamos, NM, 87545, USA.
¹¹ Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA.
¹² Department of Physics & Engineering Physics, University of Saskatchewan, Saskatoon, SK, S7N 5E2, Canada.
¹³ Department of Physics & Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada. [email protected].
¹⁴ Quantum Matter Institute, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada. [email protected].

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, v_Sm, in the Sm_xLa_1-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 v_Sm ~ 2; surprisingly, by further reducing x, a re-entrant increase of v_Sm develops, approaching the value of v_imp ~ 2.35 in the dilute-impurity limit. Such behaviour departs from a monotonic evolution of v_Sm 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 Sm_xLa_1-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.