Electron correlation effects on exchange interactions and spin excitations in 2D van der Waals materials

TL;DR

This paper demonstrates that including nonlocal electron correlations in calculations of 2D van der Waals magnetic materials like CrI$_3$ reveals new insights into spin excitations and gap mechanisms, emphasizing the importance of electron correlations.

Contribution

The study introduces a correlation-enhanced interlayer super-superexchange mechanism that explains spin excitation features in CrI$_3$, challenging previous spin-orbit-based explanations.

Findings

Electron correlations significantly influence spin excitations.

Identification of a correlation-driven interlayer super-superexchange.

Discovery of a correlation-induced gap in the magnon spectrum.

Abstract

Despite serious effort, the nature of the magnetic interactions and the role of electron-correlation effects in magnetic two-dimensional (2D) van der Waals materials remain elusive. Using CrI$_3$ as a model system, we show that the calculated electronic structure including nonlocal electron correlations yields spin excitations consistent with inelastic neutron scattering measurements. Remarkably, this approach identifies an unreported correlation-enhanced interlayer super-superexchange, which rotates the magnon Dirac lines off, and introduces a gap along, the high-symmetry $\Gamma$-$K$-$M$ path. This discovery provides a different perspective on the gap opening mechanism observed in CrI$_3$, which was previously associated with spin-orbit coupling through the Dzyaloshinskii-Moriya interaction or Kitaev interaction. Our observation elucidates the critical role of electron correlations on the spin ordering and spin dynamics in magnetic van der Waals materials and demonstrates the necessity of explicit treatment of electron correlations in the broad family of 2D magnetic materials.