1T−TaS2charge-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 $1T_2\to 1T_3$ phase transition of Ta${\mathrm{S}}_2$ at $T\sim 200$ 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 $1T_3-\mathrm{T}\mathrm{a}{\mathrm{S}}_2$ 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.