Dirac nodal line and pseudo-gap in 1T-VS₂ single crystal

Vanadium disulfide (VS₂), one of transition metal dichalcogenide (TMDC) family, attracts elevated interests for its charge-density wave phase transition, ferromagnetism, optoelectronic switching, and catalytic reactivity, but the topological Dirac surface states have not been observed yet. Here we report the Dirac nodal line states of VS₂ single crystals via angle-resolved photoemission spectroscopy (ARPES) measurements. ARPES analysis reveals that Dirac nodal line surface states are extended from the Μ point toward the Γ point with energy of −1.1 eV. Comparison with the other vanadium chalcogenides shows monotonic energy shift of the Dirac states depending on the spin-orbit coupling strength of the chalcogen atoms. Furthermore, we studied the temperature-dependence of pseudo gaps near both the M and Γ points. Our observations provide experimental evidence of topological electronic structures, contributing to the understanding of the correlated TMDC systems and their potential in switching devices, optical saturable absorber, and electrocatalysis.