Tunability of the topological nodal-line semimetal phase in ZrSiX -type materials ( X=S, Se, Te )

The discovery of a topological nodal-line (TNL) semimetal phase in ZrSiS has invigorated the study of other members of this family. Here, we present a comparative electronic structure study of $\mathrm{ZrSi}X$ (where $X=\text{S}$, Se, Te) using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Our ARPES studies show that the overall electronic structure of $\mathrm{ZrSi}X$ materials comprises the diamond-shaped Fermi pocket, the nearly elliptical-shaped Fermi pocket, and a small electron pocket encircling the zone center ($\mathrm{\Gamma }$) point, the $M$ point, and the $X$ point of the Brillouin zone, respectively. We also observe a small Fermi surface pocket along the $M-\mathrm{\Gamma }-M$ direction in ZrSiTe, which is absent in both ZrSiS and ZrSiSe. Furthermore, our theoretical studies show a transition from nodal-line to nodeless gapped phase by tuning the chalcogenide from S to Te in these material systems. Our findings provide direct evidence for the tunability of the TNL phase in $\mathrm{ZrSi}X$ material systems by adjusting the spin-orbit coupling strength via the $X$ anion.