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

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We present electrical resistivity (ρ) measurements for the intercalation compound Fex TiSe2 (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 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×2a×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< xc ≤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).
2006-02-16