Fig. 2: Band structure of CsV₃Sb₅ and Ta substituted CsV₃Sb₅ measured at low temperature (25 K).

a, b Photoelectron intensity plots along Γ-K-M-Γ of CsV₃Sb₅ (a) and CsV_2.6Ta_0.4Sb₅ (b) measured with 56 eV circularly polarized photons. c, d Calculated orbital-resolved band structure along Γ-K-M-Γ of CsV₃Sb₅ (c) and Ta substituted CsV₃Sb₅ (d). Two Ta atoms are considered in a 2 × 2 supercell to simulate the Ta substituted sample. Different orbitals are marked by different colors. The size of the markers represents the spectral weight of the orbitals. The electron-like band near Γ mainly consists of the Sb p_z orbital, the Dirac cone around K is primarily contributed by V/Ta d_xy and \({d}_{{x}^{2}{-y}^{2}}\) orbitals, and the low energy VHS near M is dominated by the V/Ta \({d}_{{z}^{2}}\) orbital with contributions from the V/Ta d_xy orbital. e Schematic of the BZ in the Γ-K-M plane. Arrows indicate the locations of the momentum cuts. f, g Photoelectron intensity plots along Γ-K-M-Γ of CsV_2.6Ta_0.4Sb₅ measured with 56 eV linear horizontally (LH) polarized (f) and linear vertically (LV) polarized (g) light. Dashed lines in (f), (g) are the eye-guide for orbitals probed by each polarization, respectively. h MDC-derived dispersion of the electron-like band around Γ in the boxed area in (a). λ^’ marks the effective coupling strength. The ratio between the high-energy velocity above the kink energy (purple) and the dressed velocity below the kink energy (pink) is defined as λ^’+1. Full-width-at-half-maximum (FWHM) of the MDC peaks is shown in the inset. i Same as (h), but extracted from the CsV_2.6Ta_0.4Sb₅ data in (b).