Layer-Resolved Magnetic Proximity Effect in van der Waals Heterostructures (2001.03861v1)

Abstract: Magnetic proximity effects are crucial ingredients for engineering spintronic, superconducting, and topological phenomena in heterostructures. Such effects are highly sensitive to the interfacial electronic properties, such as electron wave function overlap and band alignment. The recent emergence of van der Waals (vdW) magnets enables the possibility of tuning proximity effects via designing heterostructures with atomically clean interfaces. In particular, atomically thin CrI3 exhibits layered antiferromagnetism, where adjacent ferromagnetic monolayers are antiferromagnetically coupled. Exploiting this magnetic structure, we uncovered a layer-resolved magnetic proximity effect in heterostructures formed by monolayer WSe2 and bi/trilayer CrI3. By controlling the individual layer magnetization in CrI3 with a magnetic field, we found that the spin-dependent charge transfer between WSe2 and CrI3 is dominated by the interfacial CrI3 layer, while the proximity exchange field is highly sensitive to the layered magnetic structure as a whole. These properties enabled us to use monolayer WSe2 as a spatially sensitive magnetic sensor to map out layered antiferromagnetic domain structures at zero magnetic field as well as antiferromagnetic/ferromagnetic domains near the spin-flip transition in bilayer CrI3. Our work reveals a new way to control proximity effects and probe interfacial magnetic order via vdW engineering.

Layer-Resolved Magnetic Proximity Effect in van der Waals Heterostructures

The paper "Layer-Resolved Magnetic Proximity Effect in van der Waals Heterostructures" presents an in-depth exploration of the magnetic proximity effects in heterostructures composed of monolayer WSe$_2$ and bilayer/trilayer CrI$_3$. It elucidates new dimensions in manipulating interfacial magnetic orders via van der Waals (vdW) engineering. This research is significant as it details the intricate nature of spin-dependent charge transfer and proximate exchange fields in atomically thin materials, which are crucial for advancing spintronic, superconducting, and topological applications.

The paper adopts a methodological approach by conducting magneto-optical spectroscopy, specifically polarization-resolved magneto-photoluminescence, alongside reflective magnetic circular dichroism (RMCD) experiments, to probe the underlying magnetic dynamics. These techniques allowed for an atomically resolved investigation of the magnetic states of CrI$_3$, focusing on the interactions at the WSe$_2$/CrI$_3$ interface.

Key Findings

The findings reveal that the spin-dependent charge transfer between WSe$_2$ and CrI$_3$ predominantly originates from the interfacial CrI$_3$ layer. However, the nature of the proximity exchange field showed a complex dependence on the layered magnetic configuration of CrI$_3$. This counterintuitive result highlights the nuanced influence of interlayer magnetic states, such as antiferromagnetic (AFM) and ferromagnetic (FM) domains, on the electronic phenomena in attached nonmagnetic layers.

1. Spin Dynamics and Charge Transfer: The research confirms that the spin-polarized state of the interfacial layer governs the charge transfer dynamics. It is particularly elucidated that spin-dependent charge transfer is modulated significantly by the magnetic state, implying that real-space electron hopping is a critical mechanism.
2. Proximity Exchange Field: The paper further uncovers that the proximate exchange field is significantly amplified in AFM states compared to FM configurations—unexpected for a proximity effect typically reliant on the topmost magnetic layer's magnetization due to short-range interactions.
3. Imaging Magnetic Domains: Utilizing the unique properties of WSe$_2$ as a spatially sensitive sensor, the researchers successfully mapped magnetization dynamics within CrI$_3$ layers. This offers a novel pathway to detect antiferromagnetic domains that were previously elusive to traditional magnetometry techniques.

Implications and Future Work

The implications of these findings are multifaceted. From a practical perspective, the ability to manipulate and probe layered magnetic orders in vdW heterostructures suggests new directions for developing spintronic devices with more precise control over magnetic properties. Given the observed sensitivity to AFM configurations, these materials may serve as potential platforms for both designing advanced spintronic devices and fundamental studies in condensed matter physics.

From a theoretical standpoint, the observed phenomena challenge existing understandings of magnetic proximity effects and emphasize the need for more detailed theoretical models. The paper proposes that strain engineering could be an avenue to further control the magnetic states, given the notable strain-induced domain behaviors reported.

Finally, future investigations ought to focus on the precise determination of parameters such as hopping elements and band offsets, potentially through angle-resolved photoemission spectroscopy and advanced modeling. Additionally, the implications of domain pinning and reconfiguration offer an exciting landscape for experimental inquiries into the mechanical control of magnetic properties via vdW engineering.