Direct observation of the orbital state in Lu2 V2 O7: A V51 NMR study

The orbital ordering of a vanadium pyrochlore compound Lu2 V2 O7 was investigated by V51 NMR measurements. With rotation of a single crystal of Lu2 V2 O7 in an external magnetic field, NMR spectra show a characteristic angle dependence reflecting V 3d orbital states and clearly identify the orbital ordering of Lu2 V2 O7. The large anisotropy of the hyperfine field represents the fact that the quadrupole moment of 3d electrons is almost fully polarized and that the orbital fluctuation is almost quenched in the ground state. The temperature dependence of the NMR spectra indicates that the magnitude of the quadrupole moment is almost invariant below TC and that the orbital ordering would probably persist above TC.