Direct evidence of band modification and suppression of superstructure in TiSe_2 upon Fe intercalation: An angle-resolved photoemission study

摘要

We present electrical resistivity (ρ) measurements for the intercalation compound Fe_xTiSe_2 (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, TiSe_2 is a semimetal having hole pockets centered at the Γ 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 Γ point are lowered. At 50 K, band folding due to 2a X 2a X 2c 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 ρ-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).