# Comment on "Topological Nodal-Net Semimetal in a Graphene Network Structure"

## TL;DR

This paper clarifies that the bct-C40 carbon structure previously claimed to host a nodal-net semimetal is actually a nodal surface semimetal, aligning with earlier theoretical concepts.

## Contribution

It corrects the classification of bct-C40 from a nodal-net to a nodal surface semimetal, providing clarification on its topological properties.

## Key findings

- bct-C40 is a nodal surface semimetal
- The concept of nodal surface semimetal predates the original claim
- Clarifies the topological classification of bct-C40

## Abstract

Recently, a distinct topological semimetal, nodal-net semimetal, has been identified by Wang et al. through ab initio calculations [Phys. Rev. Lett. 120, 026402 (2018)]. The authors claimed that a new body-centered tetragonal carbon allotrope with I4/mmm symmetry, termed bct-C40, can host this novel state exhibiting boxed-astrisk shaped nodal nets. In this Comment, we demonstrate that bct-C40 is in fact a nodal surface semimetal, the concept of which has been proposed as early as 2016 [Phys. Rev. B 93, 085427 (2016)].

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Source: https://tomesphere.com/paper/1905.08897