Experimental band structure of1T-TiSe2in the normal and charge-density-wave phases

Abstract

We have studied the charge-density-wave phase transition of ${\mathrm{TiSe}}_2$ using photoelectron spectroscopy with high angle and energy resolution. We accurately measured the band dispersions of the Se 4p and Ti 3d bands, whose interaction is thought to be deeply involved in the phase transition. In contrast to the commonly held view that ${\mathrm{TiSe}}_2$ has a semimetallic band structure with a substantial indirect band overlap, we report the existence of a small semiconducting gap for ${\mathrm{TiSe}}_2$ in either phase. This has important implications for current efforts to establish a microscopic model of the charge-density-wave transition. At low temperatures the folding of the band structure which accompanies the formation of the charge-density-wave superlattice is seen directly in our photoemission spectra.