Instability in the t2g-band model on the pyrochlore lattice

In order to investigate a large mass enhancement of LiV2O4, I studied a realistic model Hamiltonian with consideration to orbital degeneracy as well as a geometrically frustrated lattice structure. Various types of instability upon increasing electron interaction, V, are examined at zero temperature by calculating generalized susceptibilities based on the random phase approximation. The most prominent instability is a spin density wave order accompanied by orbital polarization with a wave vector close to (pi, -pi, pi), and the critical interaction strength is of the same order as the estimate for the V atom. However, the wave vector dependence of spin fluctuations is rather weak, and other spin polarizations with different wave vectors are enhanced at the same time. The enhancement is not only in the spin sector; it is interesting that the fluctuations of orbital angular momentum are also enhanced around k = 0. This indicates the importance of orbital fluctuations in this system.