1T-TaS2 charge-density-wave metal-insulator transition and Fermi-surface modification observed by photoemission

A metal-to-insulator transition is observed using angle-resolved photoemission at the 1T21T3 phase transition of TaS2 at T200 K: a 0.125-eV band gap, d subbands, and Fermi-surface modifications occur. High-resolution (0.15-eV) Ta 4f core-level spectra from 1T3-TaS2 exhibit a charge-density-wave-induced splitting (0.73 eV) with only two narrow lines (0.25 eV full width) having an area ratio 0.70 ± 0.04, which is irreconcilable with current models that give three lines with a 6:6:1 intensity ratio. © 1981 The American Physical Society.