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N. Pontius , T. Kachel, S. Bonhommeau, K. Holldack, H. A. Dürr, C. Schüßler-Langeheine, W. Schlotter, M. Beye, A. Föhlisch, W. Wurth Magnetite (Fe3O4) is an archetypal transition metal oxide which shows a first order anomaly of the electrical conductivity when crossing Tv~120K, the Verwey transition [1]. This is associated with a structural phase transition from the cubic spinel to a distorted structure, leading to the appearance of diffraction peaks mainly characterized by the wave vectors (001) and (00½). Recent studies have demonstrated by resonant soft-x-ray diffraction (RSXD) the existence of charge and orbital ordering in magnetite at the Fe L2,3 edges in the insulating low temperature phase [2]. Orbital order was also found in RSXD at the oxygen K-edge [3]. Despite extensive efforts, however, the microscopic origin of the Verwey transition, particularly the subtle interplay between the lattice and electronic structure, still remains controversial and is matter of intense investigations. The aim of our study is to get a more detailed insight into the driving forces of the transition and the interplay of structural and electronic degrees of freedom by using time-resolved RSXD. These experiments were performed using femtosecond x-ray pulses at the FLASH facility at DESY/Hamburg. The Verwey transition is induced from the low temperature phase by rapidly heating exclusively the electronic subsystem absorbing an infrared fs-laser pulse. The subsequent temporal evolution of the orbital order is probed by RSXD at the Oxygen K-edge in (00½) geometry. In complementary time-resolved optical laser pump - THz pulse probe measurements on Fe3O4 a pulse length limited drop of the optical conductivity within ~1 ps was found. [1] E.J.W. Verwey, Nature 144, 327-328 (1939) [2] J. Schlappa et al. Phys. Rev. Lett. 100, 026406 (2008) [3] D. J. Huang et al. Phys. Rev. Lett 96, 096401 (2006) |
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