Electronic Self-Organization in the \beta -Pyrochlore Oxide CsW2O6

TL;DR

This review discusses the complex electronic phase transition in CsW2O6, highlighting self-organization of 5d electrons driven by geometric frustration, electron correlation, and structural distortions, contributing to understanding electronic phenomena in transition metal oxides.

Contribution

It provides a comprehensive overview of the electronic properties and phase transition mechanisms in CsW2O6, comparing them with related materials to deepen understanding of transition metal oxide electronics.

Findings

CsW2O6 exhibits a nonmagnetic insulating phase at 215 K.

The phase transition involves charge order, Fermi surface nesting, and trimer formation.

Multiple factors like frustration and electron correlation drive the transition.

Abstract

In this review, I present the electronic properties of the beta-pyrochlore oxide CsW2O6 and other related materials. At 215 K, CsW2O6 exhibits an electronic phase transition to a nonmagnetic insulating state, which exhibits a complex self-organization of 5d electrons. In this phase transition, various factors, such as geometrical frustration of the pyrochlore structure, moderately strong electron correlation, Jahn-Teller-like distortion, phase transition to the insulating state, and formation of chemical bonds in solids, which are powerful driving forces for achieving a wide variety of electronic properties in transition metal oxides, play important roles. In CsW2O6, the interplay of these factors has led to the emergence of an electronic phase transition that preserves the cubic symmetry, three-dimensional nesting of Fermi surfaces, a possible charge order with a fractional valence satisfying the Anderson condition, and an equilateral-triangular trimer formation by a three-centered-two-electron bond. In addition to the introduction of these unique features of CsW2O6, each of them has been compared to those of other materials to provide an overview of the electronic properties of a wide variety of related materials, which can contribute to a complete understanding of the vast and infinite electronic phenomena in transition metal oxides.