High-pressure lithium as an elemental topological semimetal

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.