![FIG. 2. (a) Volume rendered 3D ARPES stack of Pb-QFMLG with the hexagonal BZ of graphene shown by dashed red lines. A region of about 20 × 15 μm 2 was probed in real space as indicated in the underlying threshold-PEEM image. (b) π -band dispersion extracted from (a) along the KM wedge in the first BZ and fitted with a 3rd NN TB model [45] (dashed red curves). (c) Sequence of k x -k y cuts at binding energies of 3.90 eV, 2.85 eV, 1.20 eV, and at the Fermi level E F . Each cut is clipped to a single k-space quadrant and the corresponding TB contour of QFMLG (solid green, blue, and purple curves, respectively) is overlayed to the counterclockwise adjacent quadrant for better visibility of the raw data. Spectral weight is partially suppressed due to a scattering-resonance effect (gray arrows) [48,49]. (d) Energymomentum cut through the graphene Dirac cone at K, perpendicular to the K direction. Dashed red curves reproduce the TB fit according to (b). (e) A detailed determination of the Dirac-point binding energy E D for all six K points (red squares) yields a mean value E D = −9 meV (black line) with standard deviation σ = 4 meV (gray bars). (f) Averaged Dirac cone band velocity v perpendicular to K as a function of binding energy (black curve). The gray corridor gives the corresponding standard error of the mean σ v and the dashed red curve represents the 3rd NN TB model. (g) The secondary spectral cutoff at reveals a work function of 4.46 eV for Pb-QFMLG (data: red, fit: black). A reference spectrum for MLG on SiC with a ≈ 0.4 eV lower work function is also shown (yellow).](https://www.researchgate.net/publication/367677929/figure/fig2/AS:11431281116478746@1675262040191/a-Volume-rendered-3D-ARPES-stack-of-Pb-QFMLG-with-the-hexagonal-BZ-of-graphene-shown-by_Q320.jpg)
June 2022
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13 Citations
Physical Review Research
Intercalation is an established technique for tailoring the electronic structure of epitaxial graphene. Moreover, it enables the synthesis of otherwise unstable two-dimensional (2D) layers of elements with unique physical properties compared to their bulk versions due to interfacial quantum confinement. In this work, we present uniformly Pb-intercalated quasifreestanding monolayer graphene on SiC, which turns out to be essentially charge neutral with an unprecedented p-type carrier density of only (5.5±2.5)×109 cm−2. Probing the low-energy electronic structure throughout the entire first surface Brillouin zone by means of momentum microscopy, we clearly discern additional bands related to metallic 2D Pb at the interface. Low-energy electron diffraction further reveals a 10×10 Moiré superperiodicity relative to graphene, counterparts of which cannot be directly identified in the available band structure data. Our experiments demonstrate 2D interlayer confinement and associated band structure formation of a heavy-element superconductor, paving the way towards strong spin-orbit coupling effects or even 2D superconductivity at the graphene-SiC interface.
![Fig. 2(a) shows a volumetric ARPES dataset of Pb-QFMLG acquired by means of momentum microscopy in steps of 50 meV down to binding energies E > 5 eV. The corresponding ≈ 300 µm 2 real-space field of view is outlined in red in the underlying threshold-PEEM image. Adopting a characteristic crown shape, conically peaking at the six K points of the hexagonal Brillouin zone (BZ) of graphene (dashed red overlay), the sharp ARPES intensity distribution indicates a completely decoupled, quasi-freestanding graphene monolayer very close to charge neutrality. Extracted from the very same 3D dataset, the energymomentum cut of Fig. 2(b) displays the graphene π-band dispersion along the ΓKMΓ wedge in the first BZ (cf. inset). Represented by the dashed red curves, a third nearest neighbor tight binding (3rd NN TB) model [45] has been fitted to the spectral maxima [46]. Besides matching the ≈ 2.85 eV energy separation between the Dirac point E D at K and the saddle-point Van Hove singularity E VHS at M, the model describes the overall π-band course reasonably well throughout the entire probed energy-momentum range. This goes however at the expense of a physically intuitive size and ratio of the hopping parameters (γ = 3.58, −0.16, and 0.18 eV for first, second, and third NN hopping, respectively) which is similar to epigraphene at higher doping levels [47]. Fig. 2(c) presents an overview of k x -k y cuts at different binding energies relative to the Fermi level E F (as acquired directly by the NanoESCA momentum microscope). Each cut is clipped to a k-space quadrant and the respective 3rd NN TB contour as per the band structure fit of Fig. 2(b) is overlayed to the counterclockwise](https://www.researchgate.net/publication/360030477/figure/fig1/AS:1146415560568843@1650338177552/a-shows-a-volumetric-ARPES-dataset-of-Pb-QFMLG-acquired-by-means-of-momentum-microscopy_Q320.jpg)