Orbital Ordering in ferromagnetic Lu2V2O7
  We have observed the orbital ordering in the ferromagnetic Mott-insulator Lu2V2O7 by the polarized neutron diffraction technique. The orbital ordering pattern determined from the observed magnetic form factors can be explained in terms of a linear combination of wave functions |yz>, |zx> and |xy>; |0> = (1/3)^(1/2) |xy> + (1/3)^(1/2)|yz> + (1/3)^(1/2) |zx> which is proportional to |(x + y + z)^2 - r^2>; where each orbital is extended toward the center-of-mass of the V tetrahedron. We discuss the stability of the ferromagnetic Lu2V2O7, using a Hubbard Hamiltonian with these three orbitals. 
H. Ichikawa, L. Kano, M. Saitoh, S. Miyahara, N. Furukawa, J.   Akimitsu, T. Yokoo, T. Matsumura, M. Takeda and K. Hirota