Spin-orbit proximity effects in graphene-based heterostructures

The integration of the spin in charge-based electronic devices has revolutionized both sensing and memory capability in microelectronics. Further development in spintronic devices requires electrical manipulation of spin current as well as spin-charge interconversion for logic operations. Graphene has raised as an outstanding spin transporter due to its weak spin-orbit coupling (SOC). However, a strong SOC is required for an electrical control of the spin state, as in the seminal proposal of Datta and Das [1], or to achieve spin-charge interconversion, via the spin Hall effect. In this talk, I will show how SOC can be induced in graphene by proximity with another material, allowing us to manipulate spin currents.

By engineering a van der Waals heterostructure (vdWh) which combines graphene with a transition metal dichalcogenide (TMD) with strong SOC (MoS₂, WSe₂), we achieved the first unambiguous experimental demonstration of spin Hall effect in graphene [2], which survives to room temperature and can be tuned by electric field [3]. The combination of long-distance spin transport and spin Hall effect in different parts of the same material gives rise to an unprecedented spin-to-charge conversion efficiency. Interestingly, the large spin-orbit proximity in this system also allows us to electrically control spins during transport, opening up exciting opportunities for spin-based logic.

Finally, spin Hall effect up to room temperature is also achieved by combining graphene with an insulator, an evaporated Bi₂O₃ layer, arising most likely from an extrinsic mechanism [4]. With a better scalability and ease of integration to electronic devices than a graphene/TMD vdWh, we show a promising material heterostructure suitable for spin-based device applications.

[1] S. Datta and B. Das, Appl. Phys. Lett. 56, 665 (1990).
[2] C. K. Safeer at al., Nano Lett. 19, 1074 (2019).
[3] F. Herling et al. APL Mater. 8, 071103 (2020).
[4] C. K. Safeer at al., Nano Lett. 20, 4573 (2020).