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Single-spin flat bands in cobalt-supported graphene

Dr. Matteo Jugovac (Elettra – Sincrotrone Trieste, Italy)
Tuesday, 27 February 2024 12:00

Place: conference hall, IMDEA Nanociencia.


Due to the fundamental and technological implications in driving the appearance of non-trivial, exotic topological spin textures and emerging symmetry-broken phases, flat electronic bands in 2D materials, including graphene, are a hot topic in the field of spintronics.

By means of spin-resolved angle-resolved photoemission spectroscopy (ARPES) experiments combined with density functional theory (DFT) calculations, we investigated the role of europium in modifying the spin-dependent electronic properties of monolayer Gr on Co(0001). Manifold effects can be revealed: i) an enhancement of the charge transfer into Gr via Eu doping (Fig. 1 top right); ii) the existence of a spin-polarized Gr-Co hybrid state formed by positioning Eu on top or beneath the Gr monolayer in both cases with a single spin (majority) character. While in the former case, the low-dispersive parabolic Gr-Co hybrid band is observed close to Fermi energy (Fig. 1 top right), extending all over the surface Brillouin zone (SBZ), when Eu is intercalated, the π* band becomes flat (Fig. 1 bottom left); iii) the large exchange coupling due to the presence of Eu induces the splitting of the π band that crosses the 4f states into minority and majority branches bending towards higher and lower binding energies respectively, accompanied by a bandgap opening at the Dirac point of about 0.36 eV [1].

In addition, if graphene is sandwiched between two Eu layers, the europium 5d majority bands from the uppermost layer hybridize with graphene, forming single-spin electron pockets, while the hybridization of the minority Eu bands induces hybridization gaps in the π* bands of graphene. Additionally, the spin-resolved measurements reveal a noteworthy single-spin dispersionless contribution near the Fermi level, hinting at the intriguing coupling between the single-spin polarized bands of graphene and optical phonons [2]. This observation expands the understanding of the electronic structure of heavily doped graphene and suggests avenues for exploring novel optical and electronic functionalities.