Electronic structure parameters of a Dirac semi-metal NiTe₂

We study the core-level and valence band electronic structure of single crystal NiTe₂, a type-II Dirac semimetal, using soft and hard x-ray photoemission, x-ray absorption and Ni 2p−3d resonant photoemission spectroscopy to quantify electronic parameters in NiTe₂. The on-site Coulomb energy (U_dd) in the Ni 3d states is quantified from measurements of the Ni 3d single particle density of states and the two-hole correlation satellite. The Ni 2p core level and L-edge absorption spectra are analyzed by charge transfer cluster model calculations using the experimentally estimated U_dd (= 3.7 eV), and the results show that NiTe₂ exhibits a negative charge-transfer energy (∆ = -2.8 eV). The cluster model analysis of NiO L-edge x-ray absorption confirms its well-known strongly correlated charge-transfer insulator character, with U_dd = 7.0 eV and ∆ = 6.0 eV. The d-p hybridization strength T_eg for NiTe₂dd in NiTe₂ compared to NiO is not due to an increase in T_eg. The increase in dⁿ count on the Ni site in NiTe₂ by nearly one electron is attributed to negative-∆ and a reduced U_dd. The obtained parameters with U_dd >|∆|, indicate the important role of a finite repulsive U_dd in making NiTe₂ a moderately correlated p-type Dirac semi-metal.