Electric fields and substrates dramatically accelerate spin relaxation in graphene

Habib, Adela; Xu, Junqing; Ping, Yuan; Sundararaman, Ravishankar

doi:10.1103/physrevb.105.115122

Cited by 9 publications

(19 citation statements)

References 54 publications

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“…We first investigate out-of-plane and in-plane spin lifetime τ s, z and τ s, x , respectively, and their anisotropy (τ s, z /τ s, x ) at E z = 0 and 300 K. From Figure a, c, we find that (i) τ s, z and τ s, x of silicene are much longer than for germanene; (ii) large τ s, z /τ s, x (10–100) is observed for both materials, much greater than the 0.5 value for graphene. , Both phenomena may be qualitatively understood based on the EY relation (typically dominant in inversion symmetric systems). Roughly speaking, the larger τ s of silicene is mainly from the smaller b 2 compared with germanene based on their intrinsic SOC strength.…”

Section: Results and Discussionmentioning

confidence: 95%

“…Spin lifetime and the spin relaxation mechanism can be tuned by applying electric fields. , We start our theoretical study from the electric-field dependence of τ s , which is critical for the manipulation of spin relaxation.…”

Section: Results and Discussionmentioning

confidence: 99%

“…Understanding spin dynamics and transport in materials is of key importance for spintronics and information technologies, and one key metric of useful spin dynamics is τ s . Compared with graphene, for which τ s has been extensively studied, ,, the τ s of silicene and germanene have not been measured and the existing few theoretical studies were done based on relatively simple models , without realistic interactions with phonons and impurities. Recently, we developed a first-principles density-matrix (FPDM) method with quantum descriptions of the scattering processes between electron–phonon (e-ph), electron–impurities (e-i), and electron–electron to simulate spin–orbit-mediated spin dynamics in solid-state systems with arbitrary symmetry. , We applied this method to disparate materials and obtained good agreement with experiments. ,, This new method enables us to predict the τ s of silicene and germanene at finite temperatures with realistic interactions with the environment without introducing any simplified model or empirical parameters, for picosecond to microsecond time scale simulation.…”

Section: Introductionmentioning

confidence: 99%

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Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics

Takenaka

Habib

et al. 2021

Nano Lett.

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Through first-principles real-time density-matrix (FPDM) dynamics simulations, we investigated spin relaxation due to electron−phonon and electron−impurity scatterings with spin−orbit coupling (SOC) in two-dimensional Dirac materials silicene and germanene at finite temperatures. We discussed the applicability of conventional descriptions of spin relaxation mechanisms by Elliott-Yafet (EY) and D'yakonov-Perel' (DP) compared to the FPDM method, which is determined by a complex interplay of intrinsic SOC, external fields, and scattering strength. For example, the electric field dependence of the spin lifetime by FPDM is close to the DP mechanism for silicene at room temperature but similar to the EY mechanism for germanene. Because of its stronger SOC strength and buckled structure in contrast to graphene, germanene has a giant spin lifetime anisotropy and spin-valley locking effect under nonzero E z and low temperatures. More importantly, germanene has a long spin lifetime (∼100 ns at 50 K) and an ultrahigh carrier mobility, making it advantageous for spin-valleytronic applications.

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Section: Results and Discussionmentioning

confidence: 95%

Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics

Takenaka

Habib

et al. 2021

Nano Lett.

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“…Recently, with our newlydeveloped first-principles density-matrix (FPDM) dynamics approach, we studied the hBN substrate effect on spin relaxation of graphene, a weak SOC Dirac material. We found a dominant D'yakonov-Perel' (DP) mechanism and nontrivial modification of SOC fields and electronphonon coupling by substrates [8]. However, strong SOC Dirac materials can have a different spin relaxation mechanism -Elliott-Yafet (EY) mechanism [17], with only spin-flip transition and no spin precession, unlike the DP mechanism.…”

Section: Introductionmentioning

confidence: 87%

“…The spin lifetimes are simulated by our recently developed first-principles density-matrix dynamics method [6,8,18,19]. Starting from an initial state with a spin imbalance, we evolve the time-dependent density matrix ρ (t) through the quantum master equation with Lindblad dynamics for a long enough simulation time, typically from ns to µs, varying with systems.…”

Section: Methodsmentioning

confidence: 99%

Substrate Effects on Spin Relaxation in Two-Dimensional Dirac Materials with Strong Spin-Orbit Coupling

Pan

2022

Preprint

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Understanding substrate effects on spin dynamics and relaxation in two-dimensional (2D) materials is of key importance for spintronics and quantum information applications. However, the key factors that determine the substrate effect on spin relaxation, in particular for materials with strong spin-orbit coupling, have not been well understood. Here we performed first-principles real-time density-matrix dynamics simulations with spin-orbit coupling (SOC) and quantum descriptions of electron-phonon and electron-impurity scattering for the spin lifetimes of supported/free-standing germanene, a prototypical strong SOC 2D Dirac material. We show that the effects of different substrates on spin lifetime can surprisingly differ by two orders of magnitude. We find that such huge difference seems to be mostly caused by substrate-induced modifications of spin-flip scattering matrix elements, in sharp contrast to the substrate effects on weak SOC materials like graphene.

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Ab Initio Predictions of Spin Relaxation, Dephasing, and Diffusion in Solids

Xu,

Ping

2023

J. Chem. Theory Comput.

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Spin relaxation, dephasing, and diffusion are at the heart of spin-based information technology. Accurate theoretical approaches to simulate spin lifetimes (τ s ), determining how fast the spin polarization and phase information will be lost, are important to the understanding of the underlying mechanism of these spin processes, and invaluable in searching for promising candidates of spintronic materials. Recently, we develop a first-principles real-time density-matrix (FPDM) approach to simulate spin dynamics for general solid-state systems. Through the complete first-principles descriptions of light−matter interaction and scattering processes including electron−phonon, electron−impurity, and electron−electron scatterings with self-consistent spin− orbit coupling, as well as ab initio Landég-factor, our method can predict τ s at various conditions as a function of carrier density and temperature, under electric and magnetic fields. By employing this method, we successfully reproduce experimental results of disparate materials and identify the key factors affecting spin relaxation, dephasing, and diffusion in different materials. Specifically, we predict that germanene has long τ s (∼100 ns at 50 K), a giant spin lifetime anisotropy, and spin−valley locking effect under electric fields, making it advantageous for spin−valleytronic applications. Based on our theoretical derivations and ab initio simulations, we propose a new useful electronic quantity, named spin−flip angle θ ↑↓ , for the understanding of spin relaxation through intervalley spin−flip scattering processes. Our method can be further applied to other emerging materials and extended to simulate exciton spin dynamics and steady-state photocurrents due to photogalvanic effect.

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Electric fields and substrates dramatically accelerate spin relaxation in graphene

Cited by 9 publications

References 54 publications

Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics

Giant Spin Lifetime Anisotropy and Spin-Valley Locking in Silicene and Germanene from First-Principles Density-Matrix Dynamics

Substrate Effects on Spin Relaxation in Two-Dimensional Dirac Materials with Strong Spin-Orbit Coupling

Ab Initio Predictions of Spin Relaxation, Dephasing, and Diffusion in Solids

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