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

TL;DR

This study reveals that the metal-insulator transition in ferromagnetic hollandite K2Cr8O16 is driven by a Peierls instability causing structural distortion and Cr tetramer formation, providing a rare example of such transition in a fully spin-polarized system.

Contribution

The paper demonstrates that the metal-insulator transition in K2Cr8O16 is caused by a Peierls instability in a quasi-one-dimensional structure, linking structural distortion with electronic transition.

Findings

Structural distortion from tetragonal to monoclinic phase occurs at transition.

Formation of Cr tetramers below the transition temperature.

The transition is driven by a Peierls instability in the quasi-1D chains.

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.