Electronic structure of commensurate, nearly commensurate, and incommensurate phases of 1T−TaS2 by angle-resolved photoelectron spectroscopy, scanning tunneling spectroscopy, and density functional theory

Abstract

The electronic structure of $1T\ensuremath{-}\mathrm{Ta}{\mathrm{S}}_{2}$ showing a metal-insulator transition and a sequence of different charge density wave (CDW) transformations was discussed in the frame of variable temperature angle-resolved photoelectron spectroscopy (ARPES), scanning tunneling spectroscopy (STS), and density functional theory (DFT) calculations. For the commensurate charge density wave phase (CCDW) the Mott gap was estimated to be 0.4 eV and energy gaps ${\mathrm{\ensuremath{\Delta}}}_{\text{CCDW},1},\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Delta}}}_{\text{CCDW},2},\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Delta}}}_{B3\ensuremath{-}\mathit{HHB}},\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Delta}}}_{B4\ensuremath{-}B3}$ were observed. For the nearly commensurate charge density wave phase (NCCDW), the reminiscent of higher and lower Hubbard bands and a very pronounced electronic state associated with the parabolic band at the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point in the Brillouin zone were identified. The incommensurate charge density wave phase (ICCDW) showed a high value of local density of states at the Fermi level and a very pronounced edge of the metallic surface state located in the range of 0.15--0.20 eV above the Fermi level. The obtained STS and ARPES results were consistent with our theoretical calculations performed within DFT formalism including spin-orbit coupling.