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Microscopic theory of spin relaxation anisotropy in graphene with proximity-induced spin-orbit coupling
摘要： We present a microscopic theory of spin dynamics in weakly disordered graphene with uniform proximity-induced spin-orbit coupling (SOC). A time-dependent perturbative treatment is employed to derive the spin Bloch equations governing the spin dynamics at high electronic density for arbitrary ratio λSOC/η, where η is the disorder-induced quasiparticle broadening and λSOC is the largest spin-orbit energy scale. Rich scenarios are predicted, depending on a delicate competition between interface-induced Bychkov-Rashba and spin-valley interaction. In the motional narrowing regime of weak SOC (λSOC (cid:2) η), the anisotropy ratio of out-of-plane to in-plane spin lifetimes ζ = τ ⊥ s agrees qualitatively with a toy model of spins in a fluctuating SOC field proposed recently by Cummings and co-workers Phys. Rev. Lett. 119, 206601 (2017). For well-resolved SOC (λSOC (cid:2) η), the spin dynamics is characterized by fast damped oscillations with spins relaxing on the timescale of a single scattering event. In this regime, qualitatively different formulas for ζ are obtained, which can be useful to model spin transport in ultraclean van der Waals heterostructures.
关键词： spin-orbit coupling,van der Waals heterostructures,spin dynamics,Bychkov-Rashba,graphene,spin-valley interaction
更新于2025-09-04 15:30:14
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Band structure tuning and charge separation of MNX monolayers and MNX/GaS van der Waals heterostructures
摘要： Efficient charge separation and band structure tuning are very important for application to photoelectric device. Here, based on first-principles calculations, we propose two-dimensional (2D) MNX (M=Zr, Hf; X=Cl, Br, I) monolayers which can be exfoliated from the corresponding layered bulk phase due to the low cleavage energy. The phonon band structure and the mechanical analysis indicate that 2D MNX monolayers can form free-standing membranes. The calculated results suggest that 2D MNX monolayers are indirect band gap semiconductors with band gaps in the range of 1.55-3.37 eV. Among them, MNI (M=Zr, Hf) monolayers with effective charge separation and moderate band gaps would have potential application to photocatalytic water splitting. In order to realize the effective charge separation for the other MNX monolayers, MNX/GaS (X=Cl, Br) heterostructures are investigated. Our calculations reveal that MNX/GaS heterostructures are typical type-II band alignment, facilitating the separation of photogenerated carriers where electrons and holes are localized in MNX and GaS monolayers, respectively. Furthermore, the band gaps of the MNX/GaS heterostructures are obviously narrowed compared to those of the isolated constituent monolayers. In addition, the band gaps and band edge positions of MNX/GaS heterostructures can further be tuned by biaxial strain to match better with the redox potentials of water. These findings in this study not only enrich the family of 2D materials, but also demonstrate that MNI (M=Zr, Hf) monolayers and MNX/GaS heterostructures are promising candidates for photocatalytic materials.
关键词： van der Waals heterostructures,photocatalytic water splitting,band structure tuning,MNX monolayers,charge separation
更新于2025-09-04 15:30:14