Entropy chase in 5d1 double perovskites
LQMEC Synergy com Prof. Ivica Živković (École Polytechnique Fédérale de Lausanne)
26/06, 4ª feira, 15h. Ed. Principal, sala 2028 ou via Zoom: sala 871 3450 5059, senha 575478
A family of double perovskites comprises a very broad range of compounds, displaying a variety of properties and raising interest from physicists, chemists and applied scientists. In this talk I will focus on our recent work on 5d1 compounds, with an emphasis on Ba2MgReO6. Here, the magnetism arises from a single electron occupying t2g orbitals under the influence of strong spin-orbit coupling, resulting in the ground state quartet. Thermodynamic measurements reveal two features, and from resonant x-ray scattering (REXS) it is possible to associate them with long-range order of magnetic dipoles developing below 18 K and charge quadrupoles below 31 K. On the other hand, careful specific heat studies reveal that in the range 2 – 50 K recovered entropy reaches only Rln2, indicating a doublet as a ground state. Contrary to the predominant view, we show evidence of a persisting doublet-doublet gap revealed by resonant inelastic x-ray scattering (RIXS). The puzzle of the ground-state degeneracy and its relation to the observed quadrupolar order can be resolved by invoking a dynamical Jahn-Teller distortion of ReO6 octahedra.
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