Direct evidence of band modification and suppression of superstructure in TiSe2 upon Fe intercalation:: An angle-resolved photoemission study

We present electrical resistivity (rho) measurements for the intercalation compound FexTiSe2 (0 <= x < 0.16) over the temperature range from 4.2 to 300 K, and angle-resolved photoemission spectra for x=0, 0.05, and 0.14 at 50 and 250 K (or 280 K). At 250 K, TiSe2 is a semimetal having hole pockets centered at the Gamma point and electron pockets around the L points of the Brillouin zone. Upon intercalation, Fe-derived flat bands appear just below the Fermi energy, and the Se 4p derived bands forming hole pockets at the Gamma point are lowered. At 50 K, band folding due to 2ax2ax2c superlattice is observed clearly near the L point for the host and x=0.05, while it vanishes for x=0.14, consistent with the rho-T data. The critical concentration for the suppression of the superstructure (0.05 < x(c)<= 0.075) can be explained reasonably well by the percolation threshold of a two-dimensional-trianglar lattice consisting of seven Ti atoms, which is estimated to 1/14 (=0.0714).