Magnetic proximity beyond the interface: Layer-sequence-dependent exchange in WSe${}_2$/CrI${}_3$ heterostructures

Abstract

Magnetic proximity effects in transition metal dichalcogenide (TMD)/2D-magnet heterostructures are often described in terms of the magnetization of the interfacial magnetic layer. Here, we show that this picture is sufficient to describe the neutral-exciton valley splitting of the TMD, but incomplete for its hole-doped electronic structure. We study a gate-tunable van der Waals heterostructure composed of monolayer WSe${}_2$ in direct contact with trilayer CrI${}_3$. By combining spatially and helicity-resolved reflection-contrast spectroscopy with magnetic circular dichroism, we identify two distinct magnetic domains in the trilayer CrI${}_3$: one with purely antiferromagnetic interlayer coupling and one with a mixed antiferromagnetic (AFM)/ferromagnetic~(FM) coupling. In both domains, the sign of the neutral-exciton valley splitting of WSe${}_2$ switches with the magnetization reversal of the adjacent CrI${}_3$ layer. In contrast, helicity-resolved positive-trion spectroscopy of WSe${}_2$ reveals a qualitatively different response. While the AFM domain shows a strongly helicity-selective trion resonance, the mixed AFM/FM domain exhibits trion resonances in both helicities. This behavior disappears when all CrI${}_3$ layers are aligned in a parallel magnetization direction. Our results demonstrate that charged excitons are sensitive to the full layer-resolved magnetic sequence of the adjacent 2D-magnet, revealing magnetic proximity beyond the interface.

9 pages, 3 figures