Dynamic Jahn-Teller effect in the strong spin-orbit coupling regime.

Živković, Ivica; Soh, Jian-Rui; Malanyuk, Oleg; Yadav, Ravi; Pisani, Federico; Tehrani, Aria M; Tolj, Davor; Pasztorova, Jana et al. · Nat Commun · 2024

basic_science · Level V

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Abstract

Exotic quantum phases, arising from a complex interplay of charge, spin, lattice and orbital degrees of freedom, are of immense interest to a wide research community. A well-known example of such an entangled behavior is the Jahn-Teller effect, where the lifting of orbital degeneracy proceeds through lattice distortions. Here we demonstrate that a highly-symmetrical 5d<sup>1</sup> double perovskite Ba<sub>2</sub>MgReO<sub>6</sub>, comprising a 3D array of isolated ReO<sub>6</sub> octahedra, represents a rare example of a dynamic Jahn-Teller system in the strong spin-orbit coupling regime. Thermodynamic and resonant inelastic x-ray scattering experiments, supported by quantum chemistry calculations, undoubtedly show that the Jahn-Teller instability leads to a ground-state doublet, resolving a long-standing puzzle in this family of compounds. The dynamic state of ReO<sub>6</sub> octahedra persists down to the lowest temperatures, where a multipolar order sets in, allowing for investigations of the interplay between a dynamic JT effect and strongly correlated electron behavior.