S. F. Elatresh | Searcharxiv

arXiv2019

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 $\pm π$ Berry phase. Accordingly, these dense lithium phases are topological nodal loop semimetals involving a single light element.

cond-mat.mtrl-sci↗

arXiv2019

Stability and metallization of solid oxygen under high pressure

The phase diagram of oxygen is investigated for pressures from 50 to 130~GPa and temperatures up 1200 K using first principles theory. A metallic molecular structure with the $P6_3/mmc$ symmetry ($η^{'}$ phase) is determined to be thermodynamically stable in this pressure range at elevated temperatures above the $ε$(${O_8}$) phase. Long-standing disagreements between theory and experiment for the stability of $ε$(${O_8}$), its metallic character, and the transition pressure to the $ζ$ oxygen phase are resolved. Crucial for obtaining these results are the inclusion of anharmonic lattice dynamics effects and accurate calculations of exchange interactions in the presence of thermal disorder.

physics.comp-ph↗