Conduction-band electronic structure of 1T-TaS2revealed by angle-resolved inverse-photoemission spectroscopy

Abstract

We have investigated the conduction-band electronic structure of 1$T$-TaS${}_{2}$ in the incommensurate (IC) and commensurate (C) charge-density-wave (CDW) phases by means of angle-resolved inverse-photoemission spectroscopy (ARIPES) along the $\ensuremath{\Gamma}\phantom{\rule{0.28em}{0ex}}(A)--M\phantom{\rule{0.28em}{0ex}}(L)$ direction. In the ARIPES spectra for the ICCDW phase, a continuous and dispersive Ta 5$d$ band is clearly observed near the Fermi level (${E}_{\mathrm{F}}$). For the CCDW phase, on the other hand, the Ta 5$d$ band splits up and down into two manifolds around the $M\phantom{\rule{0.28em}{0ex}}(L)$ point, reflecting formation of the $\sqrt{13}\ifmmode\times\else\texttimes\fi{}\sqrt{13}$ superstructure of the Ta plane. In addition, the CCDW-ARIPES spectrum around the $M\phantom{\rule{0.28em}{0ex}}(L)$ points exhibits a shoulder structure at 0.7 eV above ${E}_{\mathrm{F}}$, ascribed to the upper Hubbard band folded from the $\ensuremath{\Gamma}\phantom{\rule{0.28em}{0ex}}(A)$ point. We have also observed an energy gap of $\ensuremath{\sim}$100 meV in the unoccupied density of states in the CCDW phase.