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

Abstract

Through First-Principles real-time Density-Matrix (FPDM) dynamics simulations, we investigate spin relaxation due to electron-phonon and electron-impurity scatterings with spin-orbit coupling in two-dimensional Dirac materials - silicene and germanene, at finite temperatures and under external fields. We discussed the applicability of conventional descriptions of spin relaxation mechanisms by Elliott-Yafet (EY) and D'yakonov-Perel' (DP) compared to our FPDM method, which is determined by a complex interplay of intrinsic spin-orbit coupling, external fields, and electron-phonon coupling strength, beyond crystal symmetry. For example, the electric field dependence of spin relaxation time is close to DP mechanism for silicene at room temperature, but rather similar to EY mechanism for germanene. Due to its stronger spin-orbit coupling strength and buckled structure in sharp contrast to graphene, germanene has a giant spin lifetime anisotropy and spin valley locking effect under nonzero Ez and relatively low temperature. More importantly, germanene has extremely long spin lifetime (~100 ns at 50 K) and ultrahigh carrier mobility, which makes it advantageous for spin-valleytronic applications.

9 pages, 4 figures

References in corpus (8)

• Germanene: a novel two-dimensional Germanium allotrope akin to Graphene and Silicene
• Graphene Spintronics
• Valley-Polarized Metals and Quantum Anomalous Hall Effect in Silicene
• JDFTx: software for joint density-functional theory
• Structural and electronic properties of germanene on MoS${}_2$
• Controlling spin relaxation in hexagonal BN-encapsulated graphene with a transverse electric field
• Proximity effects in bilayer graphene on monolayer WSe${}_2$: Field-effect spin-valley locking, spin-orbit valve, and spin transistor
• Oscillatory D'yakonov-Perel' spin dynamics in two dimensional electron gases