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arXiv · 2112.04485

Direct observation of Jahn-Teller critical dynamics at a charge-order Verwey transition

Vinícius Pascotto Gastaldo·Mala N. Rao·Alexey Bosak·Matteo d'Astuto·Andrea Prodi·Marine Verseils·Yannick Klein·Christophe Bellin·Luigi Paolasini·Adilson J. A. de Oliveira·Edmondo Gilioli·Samrath Lal Chaplot·Andrea Gauzzi
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Abstract

By means of diffuse and inelastic x-ray scattering (DS,IXS), we probe directly the charge-ordering (CO) dynamics in the Verwey system (NaMn$_3$)Mn$_4$O$_{12}$, where a peculiar quadruple perovskite structure with no oxygen disorder stabilizes a nearly full Mn$^{3+}$/Mn$^{4+}$ static charge order at $T_{\rm CO}$=175 K concomitant to a commensurate structural modulation with propagation vector ${\bf q}_{\rm CO}=(\frac{1}{2},\frac{1}{2},0)$. At $T_{\rm CO}$, the IXS spectra unveil a softening of a 35.3 meV phonon at ${\bf q}_{\rm CO}$. Lattice dynamical calculations enable us to attribute this soft phonon to a A$_g$ mode whose polarization matches the Jahn-Teller-like distortion pattern of the structural modulation. This result demonstrates that the Jahn-Teller instability is the driving force of the CO Verwey transition in (NaMn$_3$)Mn$_4$O$_{12}$, thus elucidating a long-standing controversy regarding the mechanism of this transition observed in other mixed-valence systems like magnetite.

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Vinícius Pascotto Gastaldo, Mala N. Rao, Alexey Bosak, Matteo d'Astuto, Andrea Prodi, Marine Verseils, Yannick Klein, Christophe Bellin, Luigi Paolasini, Adilson J. A. de Oliveira, Edmondo Gilioli, Samrath Lal Chaplot, Andrea Gauzzi. 2021-12-08. Direct observation of Jahn-Teller critical dynamics at a charge-order Verwey transition. https://doi.org/10.1103/physrevb.104.235114

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