Spin-Orbital Fluctuations and a large mass enhancement in LiV₂O₄

We present a scenario that the multi-component fluctuations, especially those of the spin-orbital coupled modes, lead to the mass enhancement observed in LiV_2O_4. This phenomena is possible because all these modes are fluctuating due to the geometrical frustration. To illustrate this mechanism, the t_{2g}-orbital Hubbard model on the pyrochlore lattice is studied based on the random-phase approximation. We derive the generalized susceptibility in the SU(6) spin-orbital space and calculate the free energy by using a coupling-constant integration. The estimated specific heat coefficient is of the correct order of magnitude to explain the experiment.