de Jong, S.; Kukreja, R.; Trabant, C.; Pontius, N.; Chang, C.F.; Kachel, T.; Beye, M.; Sorgenfrei, F.; Back, H.C.; Bräuer, B; Schlotter, W.F.; Turner, J.J.; Krupin, O.; Doehler, M.; Zhu, D.; Hossain, M.A.; Scherz, A.O.; Fausti, D.; Novelli, F.; Esposito, M.; Lee, W.S.; Chuang, Y.D.; Lu, D.H.; Moore, R.G.; Yi, M.; Trigo, M.; Kirchmann, P.; Pathey, L.; Golden, M.S.; Buchholz, M.; Metcalf, P.; Parmigiani, F.; Wurth, W.; Föhlisch, A.; Schüßler-Langeheine, C.; Dürr, H.A.: Speed limit of the insulator-metal transition in magnetite. Nature Materials 12 (2013), p. 882
10.1038/NMAT3718

Abstract:
As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator– metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the lowtemperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump–probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator–metal transition. We find this to be a two-step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5+-0.2 timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.