Emergent topological magnetism in Hund's excitonic insulator

TL;DR

This paper proposes a new material platform, GdGaI, where exciton condensation leads to emergent topological magnetism, specifically Skyrmion-like spin textures, revealing novel quantum states at the atomic scale.

Contribution

It introduces GdGaI as a candidate for excitonic insulator with intertwined magnetic and excitonic phases, demonstrating emergent topological spin textures due to Hund's coupling.

Findings

Emergent Skyrmion-like spin textures with 2a length scale.

Spontaneous exciton formation linked to topological magnetism.

Potential for nanoscale quantum matter applications.

Abstract

Analogous to the charged electron-electron pair condensation in superconductors, an excitonic insulator (EI) represents Fermi surface instability due to spontaneous formation and condensation of charge-neutral electron-hole pair (exciton). Unlike in superconductors, however, the charge-neutral nature of exciton makes probing emergent EI phase via macroscopic physical properties generally difficult. Here, we propose a van der Waals coupled antiferromagnetic semiconductor GdGaI (GGI) as a new material category leading to emergent multi-q magnet intertwined with spontaneous exciton formation/condensation. Before excitonic band hybridization, a simple picture for the parent electronic state consists of electron (Gd-derived 5d) and hole (Ga-derived 4p) delocalized bands, together with Gd-derived 4f localized antiferromagnets with S = 7/2 classical nature. Through intra Gd atom 4f-5d Hund's coupling, a notable finding is the emergent minimum length scale (2a) Skyrmion-like spin texture resulting from spontaneous condensation/formation of spin-polarized exciton with BCS-BEC crossover phenomenology. This discovered platform is promising for realizing valuable quantum matter on the nanoscale; our finding will provide significant insight into designing the atomic scale topological magnetism out of itinerant systems.