Quantum interference tuning of spin-orbit coupling in twisted van der Waals trilayers

Abstract

We show that in van der Waals stacks of twisted hexagonal layers the proximity induced Rashba spin-orbit coupling can be affected by quantum interference. We calculate the quantum phase responsible for this effect in graphene-transition metal dichalcogenide bilayers as a function of interlayer twist angle. We show how this quantum phase affects the spin-polarization of the graphene bands and discuss its potential effect on spin-to-charge conversion measurements. In twisted trilayers symmetries can be broken as well as restored for certain twist angles. This can be used to deduce the effects of induced spin-orbit coupling on spin-lifetime anisotropy and magnetoconductance measurements.

Twist-Angle Controlled Collinear Edelstein Effect in van der Waals Heterostructures

“…Model -Using graphene's frame of reference to define the axes, see Fig. 1a, the low-energy Hamiltonian for a twisted graphene/TMD bilayer may be written as [39,45]…”

“…The functions λ R (θ), α R (θ), and λ sv (θ) are given in Ref. [45], wherein material parameters based upon density functional theory (DFT) simulations and photoemission spectroscopy of WSe 2 and MoS 2 are used.…”

“…( 1) possesses 6-fold twist symmetry, see refs. [39,45], whilst H sv possesses the same 3-fold symmetry as the bilayer system. This oddity in the Rashba part can be understood via a simple toy model, in which we introduce different transition metal adatoms above the A and B sublattices of graphene, as done so in Ref.…”

“…Before we investigate coupled spin-charge transport phenomena in the presence of impurity scattering, it is instructive to consider the spin texture of clean eigenstates at different twist angles. Specifically, we use parameters based on DFT simulations of graphene/WSe 2 [45] in conjunction with the TMD tight-binding model of Ref. [47].…”

“…Second and more importantly let us next consider the twist dependence of the total nonequilibrium spin polarization density, S = K 2 xx + K 2 yx E x . Due to the nontrivial evolution of proximity-induced SOC with θ [35,39,45], the magnitude of current-induced spin polarization features strong tunability, with the largest spin accumulations occurring for θ ∈ [−5 However, the most striking feature of spin-current response in twisted vdW heterostructures is the possibility to realize a CEE with non-equilibrium spins pinned parallel (or antiparallel) to the applied current at critical twist angles, θ c , where α R (θ c ) = π/2 (modulo π). This is shown in Fig.…”