# Symmetry-protected metallic and topological phases in penta-materials

## TL;DR

This paper investigates the topological and symmetry-protected electronic phases in penta-materials derived from penta-graphene, revealing room-temperature nodal line metals and topological insulators through a novel topological quantum chemistry approach.

## Contribution

It introduces a new method, topological quantum chemistry, to characterize the topology of electronic bands in penta-materials, and demonstrates the emergence of metallic and topological phases under various modifications.

## Key findings

- Adsorption of alkali atoms induces a nodal line metal at room temperature.
- Substitutional derivatives like penta-PC$_2$ also exhibit similar metallic behavior.
- Magnetic atoms can break time-reversal symmetry, leading to topological insulator phases.

## Abstract

We analyze the symmetry and topological features of a family of materials closely related to penta-graphene, derived from it by adsorption or substitution of different atoms. Our description is based on a novel approach, called topological quantum chemistry, that allows to characterize the topology of the electronic bands, based on the mapping between real and reciprocal space. In particular, by adsorption of alkaline (Li or Na) atoms we obtain a nodal line metal at room temperature, with a continuum of Dirac points around the perimeter of the Brillouin zone. This behavior is also observed in some substitutional derivatives of penta-graphene, such as penta-PC$_2$. Breaking of time-reversal symmetry can be achieved by the use of magnetic atoms; we study penta-MnC$_2$, which also presents spin-orbit coupling and reveals a topological insulator phase. We find that for this family of materials, symmetry is the source of protection for metallic and nontrivial topological phases that can be associated to the presence of fractional band filling, spin-orbit coupling and time-reversal symmetry breaking.