Electronic structure of quasi-one-dimensional conductors Nb3 X4 (X=S,Se,Te) studied by angle-resolved photoemission spectroscopy

High-resolution angle-resolved photoemission spectroscopy (ARPES) has been performed on quasi-one-dimensional (1D) compounds Nb3 X4 (X=S,Se,Te). We have experimentally determined the band structure of these compounds and compared with several different band calculations. We found a fairly straight 1D Fermi surface in Nb3 Te4 (charge density wave transition temperature TCDW =110 K, superconducting transition temperature Tc =1.9 K), while the Fermi surface of Nb3 Se4 (Tc =2.4 K) and Nb3 S4 (Tc =3.8 K) shows a remarkable wiggling, indicative of the more two-dimensional-like (three-dimensional-like) character. We also found a sharp quasiparticle peak near the Fermi level (EF) at low temperatures for Nb3 S4 and Nb3 Se4, while the spectral weight near EF of Nb3 Te4 is considerably suppressed. These experimental results indicate that the anisotropy of the electronic structure remarkably changes with varying the chalcogen atom in the compounds.