Charge-spin-orbital Fluctuations in Mixed Valence Spinels: Comparative Study of AlV2O4 and LiV2O4

摘要

Mixed valence spinels provide a fertile playground for the interplay betweencharge, spin, and orbital degrees of freedom in strongly correlated electronson a geometrically frustrated lattice. Among them, AlV$_2$O$_4$ andLiV$_2$O$_4$ exhibit contrasting and puzzling behavior: self-organization ofseven-site clusters and heavy fermion behavior. We theoretically perform acomparative study of charge-spin-orbital fluctuations in these two compounds,on the basis of the multiband Hubbard models constructed by using themaximally-localized Wannier functions obtained from the ab initio bandcalculations. Performing the eigenmode analysis of the generalizedsusceptibility, we find that, in AlV$_2$O$_4$, the relevant fluctuation appearsin the charge sector in $\sigma$-bonding type orbitals. In contrast, inLiV$_2$O$_4$, optical-type spin fluctuations in the $a_{\rm 1g}$ orbital areenhanced at an incommensurate wave number at low temperature. Implications fromthe comparative study are discussed for the contrasting behavior, including themetal-insulator transition under pressure in LiV$_2$O$_4$.