Abstract
Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. Here, we report a charge-state dependency of the magnetic proximity effects between MoSe2 and CrBr3 in photoluminescence, whereby the valley polarization of the MoSe2 trion state conforms closely to the local CrBr3 magnetization, while the neutral exciton state remains insensitive to the ferromagnet. We attribute this to spin-dependent interlayer charge transfer occurring on timescales between the exciton and trion radiative lifetimes. Going further, we uncover by both the magneto-optical Kerr effect and photoluminescence a domain-like spatial topography of contrasting valley polarization, which we infer to be labyrinthine or otherwise highly intricate, with features smaller than 400 nm corresponding to our optical resolution. Our findings offer a unique insight into the interplay between short-lived valley excitons and spin-dependent interlayer tunneling, while also highlighting MoSe2 as a promising candidate to optically interface with exotic spin textures in van der Waals structures.
Highlights
Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding
In stark contrast to few-layer CrI3 and CrCl3 flakes which both exhibit antiferromagnetic interlayer ordering[4,22,28], the interlayer exchange in exfoliated CrBr3 is ferromagnetic, can depend on stacking order[7,23,24,26]. The incorporation of this emerging family of magnetic materials with optically active transition metal dichalcogenides (TMDs) is expected to combine the advantageous chiral optical selection rules and spin-valley locking of TMDs with the highly correlated and field-responsive long-range ordering inherent to magnets[17,29,30,31]
The hexagonal boron nitride (hBN) encapsulation is necessary here owing to the extreme environmental sensitivity of exfoliated CrBr3, a property shared with CrI3, in which degradation occurs rapidly under exposure to air and moisture, in a reaction catalyzed by light[34]
Summary
Semiconducting ferromagnet-nonmagnet interfaces in van der Waals heterostructures present a unique opportunity to investigate magnetic proximity interactions dependent upon a multitude of phenomena including valley and layer pseudospins, moiré periodicity, or exceptionally strong Coulomb binding. In stark contrast to few-layer CrI3 and CrCl3 flakes which both exhibit antiferromagnetic interlayer ordering[4,22,28], the interlayer exchange in exfoliated CrBr3 is ferromagnetic, can depend on stacking order[7,23,24,26] The incorporation of this emerging family of magnetic materials with optically active transition metal dichalcogenides (TMDs) is expected to combine the advantageous chiral optical selection rules and spin-valley locking of TMDs with the highly correlated and field-responsive long-range ordering inherent to magnets[17,29,30,31]. Our work highlights the importance of optical resolution when studying this new class of layered magnetic materials
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