Room temperature spin Hall effect in graphene/MoS$_2$ van der Waals heterostructures (1810.12481v1)

Abstract: Graphene is an excellent material for long distance spin transport but allows little spin manipulation. Transition metal dichalcogenides imprint their strong spin-orbit coupling into graphene via proximity effect, and it has been predicted that efficient spin-to-charge conversion due to spin Hall and Rashba-Edelstein effects could be achieved. Here, by combining Hall probes with ferromagnetic electrodes, we unambiguously demonstrate experimentally spin Hall effect in graphene induced by MoS$_2$ proximity and for varying temperature up to room temperature. The fact that spin transport and spin Hall effect occur in different parts of the same material gives rise to a hitherto unreported efficiency for the spin-to-charge voltage output. Remarkably for a single graphene/MoS$_2$ heterostructure-based device, we evidence a superimposed spin-to-charge current conversion that can be indistinguishably associated with either the proximity-induced Rashba-Edelstein effect in graphene or the spin Hall effect in MoS$_2$. By comparing our results to theoretical calculations, the latter scenario is found the most plausible one. Our findings pave the way towards the combination of spin information transport and spin-to-charge conversion in two-dimensional materials, opening exciting opportunities in a variety of future spintronic applications.

• The paper shows the emergence of a room-temperature spin Hall effect in graphene induced by proximity to MoS₂ via enhanced spin–orbit coupling.
• It uses lateral spin valves in a van der Waals heterostructure to separate spin transport from charge conversion, achieving high spin-to-charge efficiency.
• The findings open promising avenues for spintronic devices by integrating graphene’s superior transport with MoS₂’s strong spin–orbit interactions.

Room Temperature Spin Hall Effect in Graphene/MoS₂ Van der Waals Heterostructures

This research paper presents an experimental paper on the emergence of room temperature Spin Hall Effect (SHE) in graphene, induced by proximity to molybdenum disulfide (MoS₂) in a van der Waals heterostructure. The primary focus is on how transition metal dichalcogenides (TMDs), like MoS₂, can be used to enhance spin-to-charge conversion in graphene through strong spin-orbit coupling (SOC) effects, robustly verified through the proximity-induced Rashba-Edelstein effect and inverse Spin Hall Effect (ISHE).

Key Results and Experimental Methodology

The researchers have effectively demonstrated the presence of SHE in graphene up to room temperature using MoS₂, achieving unprecedented efficiency levels for the spin-to-charge voltage output. By using a graphene/MoS₂ heterostructure, the research showcases a combination of spin transport and spin-to-charge conversion in a single material, a known limitation due to differing SOC strengths necessary for transport and conversion. The proximity of MoS₂, rich in strong intrinsic SOC mechanisms, paves the way for advanced functionalities in graphene without altering its exceptional electronic transport properties.

Experimentally, the paper involves lateral spin valves (LSVs) configured with multilayer graphene and MoS₂. The setup demonstrates spin transport across the graphene channel while probing spin-orbit effects using ferromagnetic electrodes. A meticulous device configuration allows the separation of various spin-charge interconversion scenarios, thereby distinguishing between the SHE in graphene, Rashba-Edelstein effect, and the SHE in MoS₂.

Numerical Analysis and Theoretical Implications

The spin Hall angle measurements are indicative of a striking conversion efficiency, with:

• Spin Hall angle: $\theta_{SH}^{TMD/gr} \approx -4.5\%$ at 10 K, exhibiting a notable reduction at higher temperatures, down to $-0.33\%$ at 300 K.
• Spin-to-charge conversion efficiency: A pronounced increase in $\alpha_{RE}$ (up to 3.0% at 300 K if attributed to IREE), though theoretical analyses suggest a different origin.

From a theoretical standpoint, the spin Hall conductivity underpins the combination of valley-Zeeman interaction, intrinsic SOC, and the staggered potential as central to the SHE observation. The paper brings theoretical modeling and spin transport simulations in conjunction with experimental results, elucidating the impact of disorder and temperature on spin Hall scenarios.

Broader Impact and Future Prospects

The findings have substantial implications in spintronics, particularly in the development of efficient, all-electrically controlled spintronic devices, including spin-orbit torque memories and logic circuits. The use of graphene/TMD heterostructures for integrated spin transport and conversion offers a more seamless approach compared to the traditional use of heavy metals like platinum, traditionally used for their large SHE efficiencies.

The paper also opens speculation on enhancing control via external gate modifications to tune the spin-to-charge conversion strength. Additionally, extrapolating this approach to other graphene-based combinations with materials that provide giant REE could realize further significant advancements in spin-based technologies.

This research exemplifies progress in integrating two-dimensional materials with intricate spintronic mechanisms, presenting room for exploration in both experimental configurations and theoretical modeling, furthering applications in nanoscale device architectures that exceed current technological limitations.