Tanaka, A.; Chang, C.F.; Buchholz, M.; Trabant, C.; Schierle, E.; Schlappa, J.; Schmitz, D.; Ott, H.; Metcalf, P.; Tjeng, L.H.; Schüßler-Langeheine, C.: Symmetry of orbital order in Fe3O4 studied by Fe-L2,3 resonant x-ray diffraction. Physical Review Letters 108 (2012), p. 227203/1-5
10.1103/PhysRevLett.108.227203

Abstract:
We studied the symmetry of the Fe 3d wave function in magnetite below the Verwey temperature TV with resonant soft-x-ray diffraction. Although the lattice structure of the low-temperature phase of Fe3O4 is well described by the pseudo-orthorhombic Pmca with a slight monoclinic P2=c distortion, we find that the 3d wave function does not reflect the Pmca symmetry, and its distortion toward monoclinic symmetry is by far larger than that of the lattice. The result supports a scenario in which the Verwey transition involves the ordering of t2g orbitals with complex-number coefficients.