# Topological metal-insulator transition within the ferromagnetic state

## TL;DR

The paper shows a metal-insulator transition in K2Cr8O16 that is linked to topological and magnetic properties, offering insights for quantum devices.

## Contribution

The study reveals a topological metal-insulator transition within a ferromagnetic phase, driven by electronic correlations rather than phonon effects.

## Key findings

- K2Cr8O16 undergoes a metal-insulator transition within its ferromagnetic state.
- The transition is topological and not driven by the Peierls mechanism.
- Electronic correlations stabilize the insulating state with potential axionic properties.

## Abstract

A major challenge in condensed matter physics is integrating topological phenomena with correlated electron physics to leverage both types of states for next-generation quantum devices. Metal-insulator transitions are central to bridging these two domains while simultaneously serving as on-off switches for electronic states. Here, we demonstrate how the prototypical material of K2Cr8O16 undergoes a ferromagnetic metal-insulator transition accompanied by a change in band topology. Through inelastic x-ray and neutron scattering experiments combined with first-principles theoretical calculations, we show that this transition is not driven by a Peierls mechanism, given the lack of phonon softening. Instead, we establish the transition as a topological metal-insulator transition within the ferromagnetic phase with potential axionic properties, where electron correlations play a key role in stabilizing the insulating state. These results reveal how a metal-insulator transition provides a pathway through which magnetism, topology, and electronic correlations interact.

Combining topological phenomena with correlated electron physics could help enable next-generation quantum devices. Here, the authors demonstrate a topological metal-insulator transition within the ferromagnetic phase of K2Cr8O16.