For the purpose of recovering the intriguing electronic properties of freestanding graphene at a solid surface, graphene self-organized on a Au monolayer on Ni(111) is prepared and characterized by scanning tunneling microscopy. Angle-resolved photoemission reveals a gapless linear $\pi$-band dispersion near $\overline{K}$ as a fingerprint of strictly monolayer graphene and a Dirac crossing energy equal to the Fermi energy ($E_F$) within 25 meV meaning charge neutrality. Spin resolution shows a Rashba effect on the $\pi$ states with a large ($\sim 13\mathrm{meV}$) spin-orbit splitting up to $E_F$ which is independent of $\mathbf{k}$.

Graphene in spintronics is predominantly considered for spin current leads of high performance due to weak intrinsic spin–orbit coupling of the graphene π electrons. Externally induced large spin–orbit coupling opens the possibility of using graphene in active elements of spintronic devices such as the Das-Datta spin field-effect transistor. Here we show that Au intercalation at the graphene–Ni interface creates a giant spin–orbit splitting (~100 meV) of the graphene Dirac cone up to the Fermi energy. Photoelectron spectroscopy reveals the hybridization with Au 5d states as the source for this giant splitting. An ab initio model of the system shows a Rashba-split spectrum around the Dirac point of graphene. A sharp graphene–Au interface at the equilibrium distance accounts for only ~10 meV spin–orbit splitting and enhancement is due to the Au atoms in the hollow position that get closer to graphene and do not break the sublattice symmetry.

Graphene is considered a candidate material for spintronics. Recently, graphene grown on Ni(111) has been reported to show a Rashba effect which depends on the magnetization. By spin- and angle-resolved photoelectron spectroscopy, we investigate the preconditions for such an effect for graphene on Ni as well as on Co which has a $\sim 3\times$ larger $3d$ magnetic moment: (i) spin polarization or (ii) exchange splitting of graphene $\pi$ states in normal emission geometry, and (iii) Rashba-type spin-orbit splitting off normal. As none of these are found to be of considerable size, the reported effect is neither Rashba-type, nor due to the spin-orbit coupling, nor involving the electron spin.

Recently discovered intrinsic antiferromagnetic topological insulator $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ presents an exciting platform for realization of the quantum anomalous Hall effect and a number of related phenomena at elevated temperatures. An important characteristic making this material attractive for applications is its predicted large magnetic gap at the Dirac point (DP). However, while the early experimental measurements reported on large DP gaps, a number of recent studies claimed to observe a gapless dispersion of the $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ Dirac cone. Here, using micro($\mu$)-laser angle-resolved photoemission spectroscopy, we study the electronic structure of 15 different $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ samples, grown by two different chemists groups. Based on the careful energy distribution curves analysis, the DP gaps between 15 and 65 meV are observed, as measured below the Néel temperature at about 10–16 K. At that, roughly half of the studied samples show the DP gap of about 30 meV, while for a quarter of the samples the gaps are in the 50 to 60 meV range. Summarizing the results of both our and other groups, in the currently available $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ samples the DP gap can acquire an arbitrary value between a few and several tens of meV. Furthermore, based on the density functional theory, we discuss a possible factor that might contribute to the reduction of the DP gap size, which is the excess surface charge that can appear due to various defects in surface region. We demonstrate that the DP gap is influenced by the applied surface charge and even can be closed, which can be taken advantage of to tune the $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ DP gap size.