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 k space, around which an encircling k-space path is threaded by +/-pi Berry phase. Accordingly, these dense lithium phases are topological nodal loop semimetals involving a single light element.