Fig. 4: Ab initio band structure calculations.
From: Proximity induced charge density wave in a graphene/1T-TaS2 heterostructure
a Top view of graphene/1T-TaS2. Blue, brown, and yellow spheres indicate C, Ta, and S atoms, respectively. Black, blue, and brown rhombuses show the 5 × 5 graphene/√13 × √13 1T-TaS2 supercell, graphene 1 × 1 unit cell, and 1T-TaS2 1 × 1 unit cell, respectively. The calculations were carried out for a ~ 13.9° twist angle between graphene and 1T-TaS2. b Side view of graphene/1T-TaS2 overlaid with the charge density map (bubble-shaped color contour indicating the electron density) corresponding to the states at the two crossing points of the Dirac cone and Lower Hubbard band. The slight overlap between graphene and 1T-TaS2 electron clouds gives rise to the interlayer coupling and proximity effect. Here, blue, red, and green spheres represent C, Ta, and S atoms, respectively. c GGA + U spin resolved band structure of √13 × √13 CDW reconstructed 1T-TaS2 with U = 2.27 eV. d GGA + U spin resolved band structure of graphene/1T-TaS2 using the phenomenological value U = 1.70 eV. The red and blue curves are the spin-up and down bands, respectively. Owing to the charge transfer from graphene to 1T-TaS2, the Fermi level (zero energy) moves from the lower Hubbard band to the upper Hubbard band, and the graphene-associated Dirac point is shifted to ~ 0.3 eV above the Fermi level indicating hole doping. Insets on the right are zoomed in views of the bands near the upper and lower Hubbard bands. e–g The integrated DOS of graphene/1T-TaS2 in the energy range from EF to − 300 mV, − 200 mV, and + 300 mV, respectively, relative to that of freestanding graphene in corresponding energy ranges. DSs are overlaid for clarity. For the energy above the UHB (e) and below the LHB (g), the integrated DOS forms a triangular lattice. While within the Mott gap (f), the in-gap DOS forms a hexagonal lattice, in good agreement with our experimental observations in Fig. 2(g–i).
