Electronic Structures of RTe₂ (R=La,Ce): A Clue to the Pressure-Induced Superconductivity in CeTe_1.82

Electronic structures of RTe₂ (R=La,Ce) have been investigated by using the local spin density approximation (LSDA) and the LSDA+U (U: on-site Coulomb interaction) band methods. Both LaTe₂ and CeTe₂ show the very similar Fermi surface nesting features along the [100] direction, which drive the charge-density wave (CDW) instability in the Te(1) sheets. The contribution near E_F from Ce 4f states is negligible in agreement with the measured ARPES spectra. In the semimetallic CDW-distorted RTe₂, both Te vacancy and pressure induce the charge transfer from Te(1) 5p to R 5d states, producing the enhanced density of states at E_F. We suggest that these increased self-doped Te(1) 5p hole carriers are responsible for the pressure-induced superconductivity in nonstoichiometric CeTe_1.82.