Spin-orbit entanglement in two-dimensional layered materials

Abstract: Spin-orbit coupling (SOC)—a relativistic interaction which entangles a particle’s motion with its quantum mechanical spin—is fundamental to a wide range of physical phenomena, spanning from the formation of topological insulators to the spin Hall effect of light. Recent years have seen remarkable progress in the probing, enhancing and tailoring of SOC in artificial materials, specifically heterostructures, made of two or more individual flakes of graphene-like crystals arranged in a stack. From the electrical control of spin-valley coupling in bilayer graphene [1], to the reversible spin-charge conversion in graphene with proximity-induced SOC courtesy of atomically-thin semiconductors [2], these discoveries challenge our previous notions on the possible behaviour of spin-orbit coupled electrons at hetero-interfaces.

In this talk, I will show that the rich array of spin-dependent phenomena facilitated by proximity-induced SOC in graphene can be understood from the perspective of quantum information theory, i.e., as arising from quantum-mechanical entanglement between real spin and lattice-pseudospin degrees of freedom [3]. The proximity-induced SOC

and ensuing spin-spin entanglement are sensitive to the atomic registry between graphene and its high-SOC partner material, which opens up interesting possibilities for spin-charge interconversion, including a current-induced spin polarization tuneable by means of a simple interlayer rotation angle [4].

References:

[1] “Anisotropic spin currents in graphene”, https://physics.aps.org/articles/v11/s108

[2] “Proposal for unambiguous electrical detection of spin-charge conversion in lateral spin valves”, S. Cavill, C. Huang, M. Offidani, Y.-H. Lin, M. Cazalilla and A. Ferreira, Phys. Rev. Lett. 124 (2020).

[3] “Theory of spin-charge-coupled transport in proximitized graphene: an SO(5) algebraic approach”, A. Ferreira, J. Phys. Mater. 4, 045006 (2021).

[4] “Twist angle controlled collinear Edelstein effect in van der Waals heterostructures”, A. Veneri, D. Perkins, C. Péterfalvi and A. Ferreira, Phys. Rev. B 106, L081405 (2022).