Topological Metal-Insulator Transition within the Ferromagnetic state

TL;DR

This paper reports the discovery of a topological metal-insulator transition within the ferromagnetic phase of K2Cr8O16, driven by electron correlations and characterized by a change in band topology, with potential axionic properties.

Contribution

It introduces the first observation of a topological ferromagnetic metal-insulator transition, highlighting a new class of topological phase transitions involving magnetism and correlations.

Findings

Ferromagnetic MIT in K2Cr8O16 accompanied by topological change

Transition not driven by phonon softening, ruling out Peierls mechanism

Potential axionic properties associated with the transition

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 (MITs) 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 MIT accompanied by a change in band topology. Through inelastic x-ray and neutron scattering experiments combined with first-principles theoretical calculations, we demonstrate that this transition is not driven by a Peierls mechanism, given the lack of phonon softening. Instead, we establish the transition as a topological MIT within the ferromagnetic phase (topological-FM-MIT) with potential axionic properties, where electron correlations play a key role in stabilizing the insulating state. This work pioneers the discovery of a topological-FM-MIT and represents a fundamentally new class of topological phase transitions, revealing a unique pathway through which magnetism, topology, and electronic correlations interact.