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arXiv · 2511.14597

Collective modes, Yb-valence instability and metal-insulator transition in the cage-cluster borides RB12 (R- Ho, Er, Tm, Yb, Lu, Zr)

Gennady Komandin·Elena Zhukova·Boris Gorshunov·Alexander Melentyev·Ludmila Alyabyeva·Andrey Azarevich·Andrey Muratov·Yurii Aleshchenko·Nikolay Sluchanko
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Abstract

A thorough study of the wide-range (40-35000 cm-1) dynamic conductivity spectra of the rare-earth (RE) dodecaborides RB12 (R- Ho, Er and Tm) and Tm1-xYbxB12 substitutional solid solutions was carried out at room temperature. Both the Drude-type components and overdamped excitations have been separated and analyzed. An additional absorption band observed above 200 cm-1 in these RB12 with magnetic RE ions is attributed to the cooperative Jahn-Teller dynamics of the B12 complexes, which depends crucially on the RE-ion cage space and is compared with the same effect found in the non-magnetic LuB12 and ZrB12. It was shown that non-equilibrium (hot) electrons participating in the formation of the collective JT modes dominate in charge transport, and portion of Drude-type carriers changes by 20-40% in these compounds with unstable boron lattice. Strong renormalization of the infrared response is observed in Tm1-xYbxB12 solid solutions with metal-insulator transition (MIT) and is discussed in terms of localized collective modes caused by Yb-ion valence instability. We demonstrate that even at room temperature the MIT is accompanied with simultaneous decrease in concentration of Drude-type electrons and redistribution of carriers to localized JT collective modes.

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Gennady Komandin, Elena Zhukova, Boris Gorshunov, Alexander Melentyev, Ludmila Alyabyeva, Andrey Azarevich, Andrey Muratov, Yurii Aleshchenko, Nikolay Sluchanko. 2025-11-18. Collective modes, Yb-valence instability and metal-insulator transition in the cage-cluster borides RB12 (R- Ho, Er, Tm, Yb, Lu, Zr). https://arxiv.org/abs/2511.14597

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