Critical role of electron correlations on exchange interactions and spin excitations

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The intimate interplay between correlated electrons, lattice, and magnetism can result in a rich variety of interesting and important physical phenomena. In two-dimensional (2D) materials with open d- or f-shells, additional quantum confinement caused by the reduced dimensionality suppresses the screening and thus may further enhance the electron

Ke Highlight
Spinwave spectra calculated within DFT (top), and beyond DFT (bottom) compared with neutron experiments (white circles). Gap opening induced by inter-layer super-superexchange  coupling.

correlation.

Despite significant research interest, the nature of the magnetic interactions and the role of electron-correlation effects in magnetic two-dimensional (2D) van der Waals materials remains elusive. Using CrI3 as a model system, the present work addresses the critical role of electron correlation on spin ordering and dynamics in these systems. By including the nonlocal exchange-correlation, the calculated spin waves agree well with the recent inelastic neutron scattering (INS) measurements, providing by far the best ab initio description of spin excitations in CrI3.

This work identifies an unreported correlation-enhanced interlayer super-superexchange that introduces a gap along the high-symmetry Γ-K-M path. The discovery of this novel gap opening mechanism may help solve the discrepancy regarding the relativistic exchanges’ strength and their role in CrI3.

The observation of the present work elucidates the critical role of electron correlations on the magnetic interactions and spins excitations in van der Waals materials and demonstrates the necessity of explicit treatment of electron correlations in the broad family of 2D magnetic materials.

Liqin Ke and Mikhail I. Katsnelson, “Electron correlation Effects on exchange interactions and spin excitations in 2D van der Waals materials”, npj Computational Materials 7, 4 (2021); https://doi.org/10.1038/s41524-020-00469-2