Spintronics in Graphene and Other Two-Dimensional Materials
The reviewed paper provides a comprehensive overview of the advancements in spintronics with a focus on graphene and other two-dimensional (2D) materials. Since the advent of graphene, its potential for spintronics applications has garnered considerable interest, mainly due to its extraordinary electronic properties including high mobility and long spin coherence times at room temperature. The paper meticulously reviews the theoretical and experimental progress in this field, particularly emphasizing the phenomena emerging from van der Waals heterostructures and proximity-induced effects.
The paper highlights the critical milestones in the field starting from the demonstration of spin transport in graphene at room temperature, which revealed a spin relaxation length that is unprecedented in non-magnetic materials. This significant finding precipitated a surge of interest in exploring the fundamental mechanisms of spin transport within this novel material, leading to the subsequent investigation of graphene-based heterostructures with other 2D materials like hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDCs).
Among the primary mechanisms affecting spin transport, the spin-orbit coupling (SOC) in graphene remains weak, yet it is critically enhanced when graphene is coupled with other 2D materials that possess intrinsic SOC. The paper discusses how van der Waals heterostructures, particularly graphene on TMDCs, enable strong SOC, which is crucial for potential applications in spintronic devices. For example, SOC strengths up to several tens of meV have been achieved in graphene-TMDC heterostructures without compromising electron mobility, making these systems particularly attractive for studying spintronic phenomena such as the spin Hall effect.
Experimentally, a range of methodologies from electric gate-tuning to optical spin injection has been explored to manipulate spin currents in 2D materials. A notable advancement described in the paper is the integration of high-quality hBN as a substrate and tunnel barrier, which significantly improves the spin transport properties by minimizing substrate-induced scattering and contact-induced spin relaxation. This breakthrough has allowed the observation of spin transport over impressively long distances, up to tens of micrometers, within graphene channels, pointing toward its applicability in spin-based logic devices.
The implications of these advancements are vast, offering new opportunities to develop spintronic devices that operate at reduced power levels compared to traditional charge-based electronics. The theoretical predictions and experimental observations of novel spin-related phenomena enrich our understanding of quantum transport mechanisms in 2D systems and guide the optimization of spintronic devices.
Further research directions suggested by the authors include deeper explorations into the mechanisms of spin relaxation, particularly addressing the interplay between spin and pseudospin dynamics in graphene and its heterostructures. Additionally, the promising prospect of utilizing other 2D materials, including magnetic ones, broadens the horizon for developing devices with enhanced spin control capabilities.
In summary, the reviewed paper encapsulates the vast scope and rapid progression in the field of spintronics arising from 2D materials. As 2D material synthesis and 2D heterostructure technology continue to advance, the prospects for implementing these materials in practical, room-temperature spintronic devices become increasingly feasible, suggesting a transformative impact on future electronic technologies.