High-pressure lithium as an elemental topological semimetal

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 $\mathbit{k}$ space, around which an encircling $\mathbit{k}$-space path is threaded by $\ifmmode\pm\else\textpm\fi{}\ensuremath{\pi}$ Berry phase. Accordingly, these dense lithium phases are topological nodal loop semimetals involving a single light element.