Metal-insulator transition in a spin-orbital-lattice coupled Mott system:K2V8O16

Abstract

We have explored the underlying mechanism of the metal-insulator transition (MIT) in hollandite-type vanadate, ${\mathrm{K}}_{2}{\mathrm{V}}_{8}{\mathrm{O}}_{16}$, which has a quasi-one-dimensional chain structure and undergoes the MIT and Peierls-like structural transition upon cooling. For this purpose, we have investigated its electronic and magnetic properties in comparison to those of ${\mathrm{Rb}}_{2}{\mathrm{V}}_{8}{\mathrm{O}}_{16}$ that also undergoes the MIT but without the Peierls-like structural distortion. We have found that ${\mathrm{K}}_{2}{\mathrm{V}}_{8}{\mathrm{O}}_{16}$ is a spin-orbital-lattice coupled Mott system and manifests the orbital-selective Mott transition. The interplay of on-site Coulomb interaction, the magnetic-exchange interaction, and the Jahn-Teller-type tetragonal distortion plays an essential role in driving the MIT of ${\mathrm{K}}_{2}{\mathrm{V}}_{8}{\mathrm{O}}_{16}$, inducing the the charge ordering (CO) and orbital ordering of V ${t}_{2g}$ bands. The CO of $\mathrm{V}^{3+}$ and $\mathrm{V}^{4+}$ occurs in separate chains, preserving the inversion symmetry of the crystal. The ${d}_{xy}$ orbitals form the spin-singlet state along the chain direction. The Peierls-like distortion does not play an essential role in the MIT.