Electronic structure of layered transition-metal dichalcogenides Nb _1-xTi_xXc₂ (Xc = S, Se, Te) studied by angle-resolved photoemission spectroscopy

We have performed systematic high-resolution angle-resolved photoemission spectroscopy (ARPES) on layered transition-metal dichalcogenides Nb _1-xTi_xXc₂ (Xc = S, Se, Te) to study the mechanism of metal-semiconductor transition as a function of x and Xc. We found a pseudogap near E_F in the S-and Se-based compounds while a clear Fermi edge is observed in the Te-based compound. The existence of the pseudogap indicates the strong scattering of electrons by the random potential caused by substitution, which prevents formation of the charge density wave and at the same time decreases the metallic conductivity. The metallic character of Nb _1-xTi_xTe₂ is explained in terms of the relatively strong Te 5p-Nb 4d (Ti 3d) hybridization near E_F.