We study model systems with various electronic orders to understand the fundamental mechanisms at the origin of their properties as well as to investigate the interplay between the different orders (charge density wave (CDW) or charge order (CO), orbital order (OO) magnetism, and/or superconductivity).
An example : Fe3O4
Magnetite (Fe3O4) is the archetypical charge ordered system. Besides its well-known ferromagnetic properties that have been used widely in the past centuries it undergoes a metal-to-insulator phase transition at TV = 123 K, the so-called Verwey transition. The precise origin of the Verwey phase transition remains elusive yet. Our work has concentrated in understanding the role of electronic orderings (charge and orbitals) at the phase transition by means of resonant X-ray scattering. One of our major achievements has been to quantify the amount of charge that orders at the Fe-octahedral positions (Figure 1). Another point raised by our studies is the onset of long range charge and orbital correlations at a temperature where a spin-reorientation is observed (TK in Figure 2). Recently we have highlighted the role of surface strains (induced by polishing the surface of the crystal) at the onset of the transition and the occurrence of the Verwey transition through two characteristic length scales (Figure 2).
Future work aims at understanding the electronic phase separation that took place at TV by measuring the extension of the charge and orbital correlations with microfocus X-ray diffraction.
Members of the team
E. Lorenzo, P. Monceau, G. Remenyi
 Incommensurate systems as model compounds for disorder revealing low-temperature glasslike behavior, G. Reményi, S. Sahling, K. Biljaković, D. Starešinić, J.-C. Lasjaunias, J.-E. Lorenzo, P. Monceau, A. Cano, Physical Review Letters 114, 195502 (2015) [HAL,PRL]
 Spontaneous Breaking of Isotropy Observed in the Electronic Transport of Rare-Earth Tritellurides, A.A. Sinchenko, P.D. Grigoriev, P. Lejay, P. Monceau, Physical Review Letters 112, 036601 (2014) [HAL,PRL]
 Electronic Instability in a Zero-Gap Semiconductor : The Charge-DensityWave in (TaSe4)(2)I, C. Tournier-Colletta, L. Moreschini, G. Autes, S. Moser, A. Crepaldi, H. Berger, A.L. Walker, K.S. Kim, A. Bostwick, P. Monceau, E. Rotenberg, O.V. Yazyev, M. Grioni Physical Review Letters 110, 236401 (2013) [arXiv,PRL]
 Charge and orbital correlations at and above the Verwey phase transition in magnetite, J.E. Lorenzo, C. Mazzoli, N. Jaouen, C. Detlefs, D. Mannix, S. Grenier, Y. Joly and C. Marin, Phys. Rev. Lett. 101, 226401 (2008) [HAL,PRL]
 of surface polishing and oxidization induced strain on electronic order at the Verwey transtion in Fe3O4, W. Tabis, J.E Lorenzo, A. Kozlowski, T. Kolodziej, Z. Tarnawski, C. Mazzoli, H. Walker, N. Jaouen, D. Mannix, and C. Marin, J. Phys. : Condens Matter 25, 055603 (2013) [HAL,JPCM]