Topological nodal-line fermions in ZrSiSe and ZrSiTe

TL;DR

This paper reports the discovery of topological nodal-line fermions in ZrSiSe and ZrSiTe, revealing their Fermi surface characteristics, high fermion density, and potential for 2D topological insulator applications.

Contribution

It provides experimental evidence of nodal-line fermions in ZrSiSe and ZrSiTe, expanding the known materials hosting such topological states and exploring their electronic properties.

Findings

Nodal line fermions confirmed in ZrSiSe and ZrSiTe.

Fermi surface in ZrSiTe is 2D-like, unlike the 3D in ZrSiSe and ZrSiS.

High fermion density (~10^20-10^21 cm^-3) in ZrSi(S/Se).

Abstract

The discovery of topological semimetal phase in three-dimensional (3D) systems is a new breakthrough in topological material research. Dirac nodal-line semimetal is one of the three topological semimetal phases discovered so far; it is characterized by linear band crossing along a line/loop, contrasted with the linear band crossing at discrete momentum points in 3D Dirac and Weyl semimetals. The study of nodal-line semimetal is still at initial stage; only three material systems have been verified to host nodal line fermions until now, including PbTaSe2, PtSn 4and ZrSiS. In this letter, we report evidence of nodal line fermions in ZrSiSe and ZrSiTe probed in de Haas - van Alphen (dHvA) quantum oscillations. Although ZrSiSe and ZrSiTe share similar layered structure with ZrSiS, our measurements of angular dependences of dHvA oscillations indicate the Fermi surface (FS) enclosing Dirac nodal line is of 2D character in ZiSiTe, in contrast with 3D-like FS in ZrSiSe and ZrSiS. Another important property revealed in our experiment is that the nodal line fermion density in ZrSi(S/Se) (~ 10^20-10^21 cm^-3) is much higher than the Dirac/Weyl fermion density of any known topological materials. In addition, we have demonstrated ZrSiSe and ZrSiTe single crystals can be thinned down to 2D atomic thin layers through microexfoliation, which offers a promising platform to verify the predicted 2D topological insulator in the monolayer materials with ZrSiS-type structure