# High-pressure lithium as an elemental topological semimetal

## TL;DR

This paper predicts that under high pressure, certain dense lithium phases exhibit topological nodal loop semimetal properties characterized by nontrivial Berry phases, despite lithium being a light element.

## Contribution

It introduces the discovery of topological semimetal phases in high-pressure lithium polymorphs, a novel finding for a light element.

## Key findings

- High-pressure lithium phases display Fermi pockets with nontrivial topology.
- These phases are identified as topological nodal loop semimetals.
- The study reveals topological properties in a light element under extreme conditions.

## Abstract

Topological semimetals generally contain heavy elements. Using density-functional theoretic calculations, we predict that three dense lithium polymorphs in the pressure range 200--360 GPa display nontrivial semimetallic electronic structure. Specifically, these high-pressure phases exhibit Fermi pockets which are degenerate over a loop in $\boldsymbol{k}$-space, around which an encircling $\bm k$-space path is threaded by $\pm \pi$ Berry phase. Accordingly, these dense lithium phases are topological nodal loop semimetals involving a single light element.