24 \textmu m length spin relaxation length in boron nitride encapsulated bilayer graphene

We have performed spin and charge transport measurements in dual gated high mobility bilayer graphene encapsulated in hexagonal boron nitride. Our results show spin relaxation lengths $\lambda_s$ up to 13~\textmu m at room temperature with relaxation times $\tau_s$ of 2.5~ns. At 4~K, the diffusion coefficient rises up to 0.52~m$^2$/s, a value 5 times higher than the best achieved for graphene spin valves up to date. As a consequence, $\lambda_s$ rises up to 24~\textmu m with $\tau_s$ as high as 2.9~ns. We characterized 3 different samples and observed that the spin relaxation times increase with the device length. We explain our results using a model that accounts for the spin relaxation induced by the non-encapsulated outer regions.Comment: 5 pages and 4 figure

Transfer of Large-Scale Two-Dimensional Semiconductors:Challenges and Developments

Two-dimensional (2D) materials offer opportunities to explore both fundamental science and applications in the limit of atomic thickness. Beyond the prototypical case of graphene, other 2D materials have recently come to the fore. Of particular technological interest are 2D semiconductors, of which the family of materials known as the group-VI transition metal dichalcogenides (TMDs) has attracted much attention. The presence of a bandgap allows for the fabrication of high on-off ratio transistors and optoelectronic devices, as well as valley/spin polarized transport. The technique of chemical vapour deposition (CVD) has produced high-quality and contiguous wafer-scale 2D films, however, they often need to be transferred to arbitrary substrates for further investigation. In this Review, the various transfer techniques developed for transferring 2D films will be outlined and compared, with particular emphasis given to CVD-grown TMDs. Each technique suffers undesirable process-related drawbacks such as bubbles, residue or wrinkles, which can degrade device performance by for instance reducing electron mobility. This Review aims to address these problems and provide a systematic overview of key methods to characterize and improve the quality of the transferred films and heterostructures. With the maturing technological status of CVD-grown 2D materials, a robust transfer toolbox is vital

Interfacial spin-orbit torques and magnetic anisotropy in WSe₂/permalloy bilayers

Transition metal dichalcogenides (TMDs) are promising materials for efficient generation of current-induced spin-orbit torques (SOTs) on an adjacent ferromagnetic layer. Numerous effects, both interfacial and bulk, have been put forward to explain the different torques previously observed. Thus far, however, there is no clear consensus on the microscopic origin underlying the SOTs observed in these TMD/ferromagnet bilayers. To shine light on the microscopic mechanisms at play, here we perform thickness dependent SOT measurements on the semiconducting WSe2/permalloy bilayer with various WSe2 layer thickness, down to the monolayer limit. We observe a large out-of-plane field-like torque with spin-torque conductivities up to 1 × 104 (ℏ/2e) (Ωm)−1. For some devices, we also observe a smaller in-plane antidamping-like torque, with spin-torque conductivities up to 4 × 103 (ℏ/2e) (Ωm)−1, comparable to other TMD-based systems. Both torques show no clear dependence on the WSe2 thickness, as expected for a Rashba system. Unexpectedly, we observe a strong in-plane magnetic anisotropy—up to about 6.6 × 104 erg cm−3—induced in permalloy by the underlying hexagonal WSe2 crystal. Using scanning transmission electron microscopy, we confirm that the easy axis of the magnetic anisotropy is aligned to the armchair direction of the WSe2. Our results indicate a strong interplay between the ferromagnet and TMD, and unveil the nature of the SOTs in TMD-based devices. These findings open new avenues for possible methods for optimizing the torques and the interaction with interfaced magnets, important for future non-volatile magnetic devices for data processing and storage

Erratum: Interfacial spin-orbit torques and magnetic anisotropy in WSe2/permalloy bilayers

Upon further analysis of the data, we find that the field dependence of the B-component in figure 2(b) is more likely caused by a significant unidirectional magnetoresistance (UMR), hindering the accurate determination of a damping-like torque for our devices. We would like to stress that all the main conclusions of our work remain the same