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arXiv 1807.09275cond-mat.mes-hall
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邻近诱导自旋轨道耦合下石墨烯自旋弛豫各向异性的微观理论

Microscopic Theory of Spin Relaxation Anisotropy in Graphene with Proximity-Induced Spin-Orbit Coupling

Manuel Offidani, Aires Ferreira

摘要:

通过邻近效应在石墨烯中诱导相当大的自旋-轨道相互作用被确立为利用二维狄拉克费米子进行自旋电子学的成功途径。半导体过渡金属二硫属化物(TMD)是石墨烯的理想补充,因为它们具有强的内在自旋轨道耦合(SOC)和自旋/谷选择性光吸收,这允许全光学自旋注入石墨烯。在这项研究中,我们提出了一个微观理论的自旋动力学在弱无序石墨烯样品受到均匀的邻近诱导的SOC实现在石墨烯/TMD双层。采用含时微扰方法导出了高电子密度下自旋动力学的自旋布洛赫方程。各种情况下进行预测,取决于一个微妙的竞争之间的界面诱导Bychkov-Rashba和自旋谷(塞曼型)的相互作用和谷内间散射率的比率。对于弱SOC,与无序诱导的准粒子加宽相比,面外与面内自旋寿命的各向异性比$ζ=τ_{s}^{\perp}/τ_{s}^{\parallel}$在定性上与Cummings及其同事最近提出的弱波动SOC场中的自旋玩具模型一致[PRL 119,206601(2017)]。在良好分辨的SOC的相反制度中,获得了定性不同的公式,其可以在以石墨烯层中的均匀邻近诱导的SOC为特征的超净异质结构中进行测试。

英文摘要:

Inducing sizable spin--orbit interactions in graphene by proximity effect is establishing as a successful route to harnessing two-dimensional Dirac fermions for spintronics. Semiconducting transition metal dichalcogenides (TMDs) are an ideal complement to graphene because of their strong intrinsic spin--orbit coupling (SOC) and spin/valley-selective light absorption, which allows all-optical spin injection into graphene. In this study, we present a microscopic theory of spin dynamics in weakly disordered graphene samples subject to uniform proximity-induced SOC as realized in graphene/TMD bilayers. A time-dependent perturbative treatment is employed to derive spin Bloch equations governing the spin dynamics at high electronic density. Various scenarios are predicted, depending on a delicate competition between interface-induced Bychkov-Rashba and spin--valley (Zeeman-type) interactions and the ratio of intra- to inter-valley scattering rates. For weak SOC compared to the disorder-induced quasiparticle broadening, the anisotropy ratio of out-of-plane to in-plane spin lifetimes $ζ=τ_{s}^{\perp}/τ_{s}^{\parallel}$ agrees qualitatively with a toy model of spins in a weak fluctuating SOC field recently proposed by Cummings and co-workers [PRL 119, 206601 (2017)]. In the opposite regime of well-resolved SOC, qualitatively different formulae are obtained, which can be tested in ultra-clean heterostructures characterized by uniform proximity-induced SOC in the graphene layer.

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