# Topological semimetal in honeycomb lattice LnSI

## TL;DR

This paper introduces specific honeycomb lattice models that realize ideal Weyl semimetals, topological insulators, and nodal-line semimetals, providing a simpler platform to study topological phases and their potential applications.

## Contribution

It presents the first realization of topological phases in honeycomb lattices, including ideal Weyl semimetals and topological insulators, with concrete material examples like GdSI and LuSI.

## Key findings

- GdSI hosts two pairs of Weyl nodes at the Fermi level.
- LuSI is identified as a 3D strong topological insulator.
- The study proposes a new platform for exploring topological semimetals.

## Abstract

Recognized as elementary particles in the standard model,Weyl fermions in condensed matter have received growing attention. However, most of the previously reportedWeyl semimetals exhibit rather complicated electronic structures that, in turn, may have raised questions regarding the underlying physics. Here, we report for the first time promising topological phases that can be realized in specific honeycomb lattices, including ideal Weyl semimetal structures, 3D strong topological insulators, and nodal-line semimetal configurations. In particular, we highlight a novel semimetal featuring both Weyl nodes and nodal lines. Guided by this model, we demonstrated that GdSI the long perceived ideal Weyl semimetal has two pairs ofWeyl nodes residing at the Fermi level, and that LuSI (YSI) is a 3D strong topological insulator with the right-handed helical surface states. Our work provides a new mechanism to study topological semimetals, and proposes a platform towards exploring the physics of Weyl semimetals as well as related device designs.