Flat band and Lifschitz transition in long-range ordered supergraphene obtained by Erbium intercalation

A. Zaarour, V. Malesys, J. Teyssandier, M. Cranney, E. Denys, J. L. Bubendorff, A. Florentin, L. Josien, F. Vonau, D. Aubel, A. Ouerghi, C. Bena, L. Simon

Published 2022-07-25Version 1

Dispersionless energy bands in momentum space are a peculiar property gathering increasing attention for the emergence of novel photonic, magnetic, and electronic properties. Here, we explore the impact of flat bands on the electronic properties of a highly-doped graphene layer. We combine STM and angle-resolved photoemission spectroscopy (ARPES) to directly map the flat-band dispersion near the Fermi level in supergraphene obtained by ordered Erbium intercalation between a single layer graphene and SiC(0001). Very intriguingly our STM experiments reveal large areas exhibiting a homogeneous quasi free-standing (QFS) graphene layer characterized by a long-range order hexagonal superstructure with a lattice parameter of 1.40 nm, rotated by 19 degrees with respect to the original lattice. ARPES measurements show that the QFS graphene layer exhibits Dirac cones with perfect linear dispersion up to the Fermi level, and a very high level of n-doping (Dirac point at -1.72 eV +/- 0.02 under the Fermi level), which is one of the highest doping level ever obtained solely by intercalation. Fermi surface measurements indicate that the Lifshitz transition in this supergraphene structure has been reached, and that a flat band is generated around the M point. We propose that this modification of the band structure is the effect of an induced spin-orbit coupling. This system realized with intercalated ordered Erbium provides a playground to study the interaction between a novel magnetic order mediated by pi-band states, and a divergent density of states at the Fermi level.