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(a) Measured band structure curve of BST along the Γ point taken at a photon energy of 60 eV. A single Dirac cone was clearly resolved and no conduction band was observed. The Dirac point (DP) is located ∼0.3 eV away from the Fermi level. (b) Photo-energy-dependent band structure curves of BST at different excitation photon energies of 80, 74, 68, 62, 56, 50, 46, and 38 eV, respectively.
