Interlayer Exchange Interaction Driven Topological Phase Transition in Antiferromagnetic Electride Gd$_2$O

TL;DR

This paper reports the discovery of a 2D antiferromagnetic electride Gd$_2$O that exhibits a topological phase transition driven by interlayer exchange interactions, leading to magnetic Dirac semimetal states with potential for novel quantum phenomena.

Contribution

It introduces a new 2D antiferromagnetic electride material Gd$_2$O with unique interlayer exchange interactions causing topological phase transitions and hosting Dirac fermions.

Findings

Gd$_2$O$ is a layered antiferromagnetic electride with interstitial electrons.

Interlayer superexchange induces coupled magnetic, structural, and electronic phase transitions.

The material hosts both massless and massive Dirac fermions protected by nonsymmorphic symmetry.

Abstract

Based on first-principles calculations, we discover a two-dimensional layered antiferromagnetic (AFM) electride Gd$_2$O, where anionic excess electrons exist in the interstitial spaces between positively charged cationic layers. It is revealed that each cationic layer composed of three-atom-thick Gd$-$O$-$Gd stacks has in-plane ferromagnetic and out-of-plane AFM superexchange interactions between the localized Gd 4$f$ spins through O 2$p$ orbitals. Furthermore, the interlayer superexchange mediated by the hybridized Gd-5$d$ and interstitial-$s$-like states involves intimate couplings between the spin, lattice, and charge degrees of freedom, thereby inducing simultaneous magnetic, structural, and electronic phase transitions. The resulting ground state with the simple hexagonal lattice hosts massless Dirac fermions protected by nonsymmorphic magnetic symmetry, as well as massive Dirac fermions. We thus demonstrate that the anionic excess electrons in Gd$_2$O play a crucial role in the emergence of magnetic Dirac semimetal states, therefore offering an intriguing interplay between 2D magnetic electrides and topological physics.