Stephan Roche & Sergio O. Valenzuela – Institut Català de Nanociència i Nanotecnologia (ICN2)

Spin is a fundamental quantum property of particles which behaves similarly to a permanent magnet attached to the quantum object and takes two values + or – half the Planck constant. Spin Hall effect (SHE) is a fundamental mechanism occurring in strong spin-orbit materials and which manifests as an accumulation of up and down spins at the opposite edges of a sample, upon the application of an electrical field. SHE actually converts charge to pure spin current in the direction perpendicular to the charge flow. The great challenge for developing spin-based informationprocessing technologies requires optimizing the spin Hall angle which measures the strength of SHE. The further use of graphene and other two-dimensional materials has sparked great expectations for the design of innovative heterostructures of superior spintronic performances which could be used in improving STT-MRAM (spin transfertorque magnetic random access memories) technologies or engineering new spin logic architectures.

Large values of SHE have been recently reported in graphene decorated with adatoms but those experiments have raised a considerable debate, given the complexity of the underlying phenomenon and multiplicity of parasitic background effects. In collaboration with researchers in the USA and France, we have performed the first fully quantum simulation of the fundamental characteristics of SHE able to revisit these controversial experimental results. We have succeeded in computing the spin Hall angle in large scale disordered forms of chemically functionalized graphene and have analysed how such quantity scales with the density of chemical defects, their spatial distribution and segregation, temperature and device geometry effects.

Our results suggest substantial capability of graphene for generating large SHE signals provided an atomic-scale control of chemical modification of graphene is achieved, whereas new device geometry has been proposed to reduce parasitic effects and quantitatively size the maximum charge to current conversion efficiency of such twodimensional materials.


Van Tuan D, Marmolejo-Tejada JM, Waintal X, Nikoli? BA, Valenzuela SO & Roche S 2016, ‘Spin Hall Effect and Origins of Nonlocal Resistance in Adatom-Decorated Graphene’, Physical Review Letters, 117, 176602.