Electronic structures of layered Ta2NiS5 single crystals revealed by high-resolution angle-resolved photoemission spectroscopy

Using high-resolution angle-resolved photoemission spectroscopy (ARPES), we systematically studied the electronic structures of quasi-one-dimensional (1D) ternary material Ta2NiS5 single crystals. Contrary to its sister compound Ta2NiSe5, which is a candidate material for excitonic insulators, we found that Ta2NiS5 cannot realize the ground state of an excitonic insulator according to temperature-dependent valence band dispersions along the Γ–X direction. In particular, the experimental ARPES data reveal that the electronic structures show strong two-dimensional characteristics along with a considerable in-plane anisotropy indicating evident coupling among the one-dimensional chain structures. Moreover, theoretical band calculations have to be compressed by a factor of about 15% in energy in order to match the experimental band structures, implying that some weak electron correlations are neglected in the band calculations.