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

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

Abstract: By means of diffuse x-ray scattering (DS) and inelastic x-ray scattering (IXS), we probe directly the chargeordering (CO) dynamics in the Verwey system (NaMn3)Mn4O12, where a peculiar quadruple perovskite structure with no oxygen disorder stabilizes a nearly full Mn3+/Mn4+ static charge order at TCO = 175 K concomitant to a commensurate structural modulation with propagation vector qCO = ( 1/2 , 1/2 , 0). At TCO, the IXS spectra unveil a softening of a 35.3-meV phonon at qCO. Lattice dynamical calculations enable us to attribute this soft phonon to an Ag 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 (NaMn3)Mn4O12, thus elucidating a long standing controversy regarding the mechanism of this transition observed in other mixed-valence systems like magnetite.

Authors: 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 and Andrea Gauzzi.

PHYSICAL REVIEW B

104, 235114 (2021)

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

DOI: : 10.1103/PhysRevB.104.235114