Unveiling giant Rashba splitting in graphene via in situ cryogenic copper adatom deposition and multimodal characterization

Abstract

Enhancing spin–orbit interaction (SOI) in graphene is a critical step toward realizing graphene-based spintronic devices, yet it has remained experimentally challenging. In this work, we employ in situ cryogenic deposition of copper adatoms on graphene to overcome previous limitations and achieve a controlled, well-defined interface. Through a multimodal approach combining magnetotransport, spin- and angle-resolved photoelectron spectroscopy (spin-ARPES), scanning tunneling microscopy, low-energy electron diffraction, x-ray photoelectron spectroscopy, and density functional theory (DFT), we provide unambiguous evidence of giant Rashba splitting in graphene. Magnetotransport measurements reveal electron doping, signatures of magnetism, and SOI enhancement, with an extracted Rashba strength of λBR≈ 1–2 meV at 0.1–0.2 monolayers (MLs) Cu coverage. Spin-ARPES directly confirms a giant Rashba splitting of ∼50 meV/8 meV for lower/upper Dirac cone at 0.5 ML Cu coverage. Furthermore, ARPES reveals the formation of flat bands near the Γ¯ point, their hybridization with graphene's π states, and quantifies the charge transfer efficiency of η=0.14. Our comprehensive experimental study, supported by our DFT calculations, resolves the long-standing theory-experiment discrepancy in adatom-induced SOI and establishes copper functionalization as a powerful method for tailoring graphene's spin properties.