Peierls Mechanism of the Metal-Insulator Transition in Ferromagnetic Hollandite K2Cr8O16

Abstract

Synchrotron X-ray diffraction experiment shows that the metal-insulator transition occurring in a ferromagnetic state of a hollandite K${}_2$Cr${}_8$O${}_{16}$ is accompanied by a structural distortion from the tetragonal $I4/m$ to monoclinic $P112_1/a$ phase with a $\sqrt{2}\times \sqrt{2}\times 1$ supercell. Detailed electronic structure calculations demonstrate that the metal-insulator transition is caused by a Peierls instability in the quasi-one-dimensional column structure made of four coupled Cr-O chains running in the $c$-direction, leading to the formation of tetramers of Cr ions below the transition temperature. This furnishes a rare example of the Peierls transition of fully spin-polarized electron systems.

Phys. Rev. Lett., in press, 5 pages, 3 figures