Abstract
Graphene offers long spin propagation and, at the same time, a versatile platform to engineer its physical properties. Proximity-induced phenomena, taking advantage of materials with large spin-orbit coupling or that are magnetic, can be used to imprint graphene with large spin-orbit coupling and magnetic correlations. However, full understanding of the proximitized graphene and the consequences on the spin transport dynamics requires the development of unconventional experimental approaches. The investigation of the spin relaxation anisotropy, defined as the ratio of lifetimes for spins pointing out of and in the graphene plane, is an important step in this direction. This review discusses various methods for extracting the spin relaxation anisotropy in graphene-based devices. Within the experimental framework, current understanding on spin transport dynamics in single-layer and bilayer graphene is presented. Due to increasing interest, experimental results in graphene in proximity with high spin-orbit layered materials are also reviewed.
Highlights
Two-dimensional (2D) materials are envisioned as fundamental building blocks for generation nanoelectronic devices, offering promising prospects and a vast number of potential applications.1 Among 2D materials, graphene, a material made of carbon atoms arranged in a honeycomb lattice, is relevant due to its structural stability and superior electronic properties.2,3 Graphene is promising for spin-based devices in which the electron spin degree of freedom, as opposed to its charge, plays a central role.4,5 The weak intrinsic spin-orbit coupling (SOC) in graphene (12 μeV) and the lack of hyperfine interaction (99% of 12C nuclei in which the nuclear spin is zero) ensure that spins propagate coherently through the crystal lattice over long distances.6–8 Such an intrinsic property has motivated many experimental and theoretical studies over the last ten years
Spin-orbit scattering times are extracted from quantum corrections to the magnetoconductivity, the most notable signature being a decrease in the spin lifetime to the picosecond range
Future experiments will aim at identifying intrinsic spin relaxation in graphene, without the presence of dominant magnetic scattering centers, and at achieving full control of the spin dynamics by manipulating the SOC with external electric fields
Summary
Two-dimensional (2D) materials are envisioned as fundamental building blocks for generation nanoelectronic devices, offering promising prospects and a vast number of potential applications. Among 2D materials, graphene, a material made of carbon atoms arranged in a honeycomb lattice, is relevant due to its structural stability and superior electronic properties. Graphene is promising for spin-based devices in which the electron spin degree of freedom, as opposed to its charge, plays a central role. The weak intrinsic spin-orbit coupling (SOC) in graphene (12 μeV) and the lack of hyperfine interaction (99% of 12C nuclei in which the nuclear spin is zero) ensure that spins propagate coherently through the crystal lattice over long distances. Such an intrinsic property has motivated many experimental and theoretical studies over the last ten years. When there is no preferential direction in the spin relaxation, as in the case of spin relaxation driven by paramagnetic impurities or (random) gauge fields, the relaxation becomes isotropic with τs⊥ = τs∥, so ζ = 1.15,16 Given that the SOFs in graphene can be altered using compounds with large SOC, spin-relaxation anisotropy is a crucial parameter to investigate spin-orbit proximity effects. The aim of this Research Update is to provide a comprehensive overview of the current experimental progress toward understanding spin relaxation phenomena in graphene-based devices by means of spin relaxation anisotropy experiments. Future experiments to further advance the understanding of spin related phenomena in these systems are discussed
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