GdI_2: A New Ferromagnetic Excitonic Solid?

TL;DR

GdI_2 is a 2D material exhibiting a transition from a ferromagnetic, metallic state to an insulating, excitonic solid, driven by geometric frustration and electron correlations, with specific experimental predictions for its unique ground state.

Contribution

This paper proposes GdI_2 as a candidate for a ferromagnetic excitonic liquid and predicts a transition to a charge-ordered excitonic solid driven by symmetry breaking.

Findings

GdI_2 exhibits a ferromagnetic metallic state at intermediate temperatures.

A transition to an insulating, excitonic solid state is predicted at low temperatures.

Experimental signatures of the excitonic solid ground state are proposed.

Abstract

The two-dimensional, colossal magnetoresistive system GdI_2 develops an unusual metallic state below its ferromagnetic transition and becomes insulating at low temperatures. It is argued that this geometrically frustrated, correlated poor metal is a possible candidate for a ferromagnetic excitonic liquid. The renormalized Fermi surface supports a further breaking of symmetry to a charge ordered, excitonic solid ground state at lower temperatures via order by disorder mechanism. Several experimental predictions are made to investigate this unique orbitally correlated ground state.