Abstract
The interconversion between spin and charge degrees of freedom offers incredible potential for spintronic devices, opening routes for spin injection, detection, and manipulation alternative to the use of ferromagnets. The understanding and control of such interconversion mechanisms, which rely on spin–orbit coupling, is therefore an exciting prospect. The emergence of van der Waals materials possessing large spin–orbit coupling (such as transition metal dichalcogenides or topological insulators) and/or recently discovered van der Waals layered ferromagnets further extends the possibility of spin-to-charge interconversion to ultrathin spintronic devices. Additionally, they offer abundant room for progress in discovering and analyzing novel spin–charge interconversion phenomena. Modifying the properties of van der Waals materials through proximity effects is an added degree of tunability also under exploration. This Perspective discusses the recent advances toward spin-to-charge interconversion in van der Waals materials. It highlights scientific developments which include techniques for large-scale growth, device physics, and theoretical aspects.
Highlights
The path to technological implementation is long and hard, the extraordinary burst of 2D material synthesis during the last decade allowed for the fabrication of a wide variety of 2D materials,[1,3] opening thrilling avenues for the design of innovative atomically flat devices. 2D materials possess strong covalent bonds between atoms in the plane, but their out-of-plane interaction is mediated by 1000 times weaker van der Waals forces, which enables an easy delamination of these layered materials
These range from the use of recently discovered 2D magnetic materials (CrSe2, VSe2, etc.) to the exploitation of the spin–charge interconversion (SCI) that takes place in materials with large spin–orbit coupling (SOC), among which we find transition metal dichalcogenides (TMDs) semimetals and topological insulators (TIs)
Epitaxy was reported for a variety of TMDs and TMD heterostructures, including MoSe2, WSe2, HfSe2, PtSe2, VSe2, ZrTe2, MoTe2, and WTe2.66,135–149 Inert van der Waals (vdW) surfaces, such as graphene, mica, or hBN, make it possible to stabilize very flat monolayers of high structural quality, as shown for mica/WSe2.149 the weak interfacial interaction often results in an in-plane misorientation of crystal grains, which probably remains the main difficulty in the Molecular beam epitaxy (MBE) of TMD monolayers
Summary
In the search for continued miniaturization of microelectronic devices, two-dimensional (2D) materials, such as graphene and its siblings, offer opportunities to radically change the technology landscape by enabling the discovery of revolutionary device paradigms.[1,2] the path to technological implementation is long and hard, the extraordinary burst of 2D material synthesis during the last decade allowed for the fabrication of a wide variety of 2D materials,[1,3] opening thrilling avenues for the design of innovative atomically flat devices. 2D materials possess strong covalent bonds between atoms in the plane, but their out-of-plane interaction is mediated by 1000 times weaker van der Waals (vdW) forces, which enables an easy delamination of these layered materials. Among the vast catalog of novel 2D materials, TMDs stand out as a versatile platform for the advancement of disruptive flat microelectronics and spintronics.[5,6,11,46,47,48] in contrast to graphene, TMDs have a large SOC49–51 that was successfully exploited for gate-controlled spin manipulation in graphene/TMD interfaces.[25,26,52] In addition, some TMDs, such as WS2 and MoS2, possess a large bandgap that promotes optoelectronic operation[53,54] and the realization of light-driven spin–valley coupling.[55,56,57,58,59,60] Beyond the most commonly found semiconducting phase, the TMD family exhibits a wide variety of electronic behaviors ranging from a Weyl semi-metallic state[61,62,63] to superconductivity[64,65] as well as magnetism.[66] These features are appealing for the realization of vdW heterostructures[50,51] that could combine all of them.[25,26] Another important class of vdW materials concern bismuthantimony chalcogenides that display topological properties. The complexity of the studied phenomena and the continued surge of new materials make synergy between experiment and theory useful in developing improved large-scale growth methods of such vdW materials to facilitate their implementation in upcoming technologies
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