Giant spin Hall effect in graphene grown by chemical vapour deposition.

Jayakumar Balakrishnan,Jong-Hyun Ahn,Barbaros Özyilmaz,Antonio H Castro Neto,Manu Jaiswal,Gavin Kok Wai Koon,Ahmet Avsar,Yuda Ho,Miguel A Cazalilla,Seung-Jae Baeck,Jong Hak Lee,Aires Ferreira

doi:10.1038/ncomms5748

Abstract

Advances in large-area graphene synthesis via chemical vapour deposition on metals like copper were instrumental in the demonstration of graphene-based novel, wafer-scale electronic circuits and proof-of-concept applications such as flexible touch panels. Here, we show that graphene grown by chemical vapour deposition on copper is equally promising for spintronics applications. In contrast to natural graphene, our experiments demonstrate that chemically synthesized graphene has a strong spin-orbit coupling as high as 20 meV giving rise to a giant spin Hall effect. The exceptionally large spin Hall angle ~0.2 provides an important step towards graphene-based spintronics devices within existing complementary metal-oxide-semiconductor technology. Our microscopic model shows that unavoidable residual copper adatom clusters act as local spin-orbit scatterers and, in the resonant scattering limit, induce transverse spin currents with enhanced skew-scattering contribution. Our findings are confirmed independently by introducing metallic adatoms-copper, silver and gold on exfoliated graphene samples.

Highlights

Advances in large-area graphene synthesis via chemical vapour deposition on metals like copper were instrumental in the demonstration of graphene-based novel, wafer-scale electronic circuits and proof-of-concept applications such as flexible touch panels
We show that the presence of dilute residual copper (Cu) adatoms on graphene grown by chemical vapour deposition (CVD) on Cu foil (CVDG)[17,18,19,20,21] is sufficient to enhance the spin–orbit coupling (SOC) strength by several orders of magnitude
The devices consists of Hall bar arrays, such that before any spin transport measurements the CVDG devices can be first characterized for charge transport using the local four-terminal geometry with Au/Cr contacts

Summary

Introduction

Advances in large-area graphene synthesis via chemical vapour deposition on metals like copper were instrumental in the demonstration of graphene-based novel, wafer-scale electronic circuits and proof-of-concept applications such as flexible touch panels. Adatom proximityinduced SOC over the nanometre scale avoids inter-valley scattering and offers a realistic route towards two-dimensional (2D) topological insulator (TI) state engineering in graphene The realization of such a quantum spin Hall/TI state in conjunction with the electric field effect in graphene is of great significance since TIs proximity coupled to superconductors are predicted to host Majorana fermions—an essential step towards topological quantum computations[6]. To rule out CVD-specific vacancies, defects and ripples for the observed enhancement in SOC, we performed identical measurements on exfoliated pristine graphene (EPG) samples that are intentionally decorated with adatoms like copper (Cu), gold (Au) and silver (Ag; see Methods for sample preparation details) In both CVDG and EPG samples decorated with metallic adatoms, we see a similar enhancement of the SOC27 by three orders of magnitude (up to 20 meV) confirming the proximity effect as the dominant cause for the observed SHE

Methods

Results

Conclusion