ORALS

In this talk we shed a light on hidden quantum properties in magnetite, the oldest magnetic material known to mankind. The study reveals the existence of low-energy waves that indicate the important role of electronic interactions with the crystal lattice as well as the lattice vibrations in both high-temperature cubic as well low-temperature monoclinic phases. This is another step to fully understand the metal-insulator phase transition mechanism in magnetite, and in particular to learn about the dynamical properties and critical behavior of this material in the vicinity of the transition temperature. The attentions of physicists in magnetite was attracted by a fact that at temperature of 125 K it shows an exotic phase transition, named after the Dutch chemist Verwey. This Verwey transition was also the first phase metal-to-insulator transformation observed historically. During this extremely complex process, the electrical conductivity changes by as much as two orders of magnitude and a rearrangement of the crystal structure takes place. Verwey proposed a transformation mechanism based on the location of electrons on iron ions, which leads to the appearance of a periodic spatial distribution of Fe2+ and Fe3+ charges at low temperatures as well as the orbital order. In this talk we confirm the fundamental components of this charge-orbital ordering are polarons – quasiparticles formed as a result of a local deformation of the crystal lattice caused by the electrostatic interaction of a charged particle (electron or hole) moving in the crystal based on the quantum-mechanical (density functional method) calculations. In the case of magnetite, the polarons take the form of trimerons, complexes made of three iron ions, where the inner atom has more electrons than the two outer atoms. Our study reveals a very accurate model of lattice vibrations for the high temperature phase as well as confirm the effect of the charge-orbital (trimeron) order on phonon energies and mean square displacements in the monoclinic(low-temperature) phase and hence to contribute to shed a light at the complexity of the Verwey transition. The work was published in [1-3].

References:
[1]E. Baldini, C.A. Belvin, M. Rodriguez-Vega, I. O. Ozel, D. Legut, A. Kozłowski, A. M. Oleś, K. Parlinski, P. Piekarz, J. Lorenzana, G. A. Fiete, and N. Gedik, Nature Physics 16 (2020), 541.
[2] S. Borroni, E. Baldini, V. M. Katukuri, A. Mann, K. Parlinski, D. Legut, C. Arrell, F. van Mourik, J. Teyssier, A. Kozlowski, P. Piekarz, O. V. Yazyev, A. M. Oleś, J. Lorenzana, and F. Carbone, Phys. Rev. B 96 (2017), 104308.
[3] P. Piekarz, D. Legut, E. Baldini, C. A. Belvin, T. Kolodziej, W. Tabi,A. Kozlowski, Z. Kakol, Z. Tarnawski, J. Lorenzana, N. Gedik, A. M. Olés, J. M. Honig, and K. Parlinski, Phys. Rev. B 103 (2021), 104303.