Optical properties of dense lithium in electride phases by first-principles calculations

TL;DR

This study uses first-principles calculations to explore the optical properties of dense lithium's electride phases under high pressure, revealing unique plasmonic features, reentrant metallicity, and anisotropic reflectivity.

Contribution

It provides detailed first-principles insights into the dielectric response and optical behavior of lithium electride phases across a wide pressure range, highlighting new plasmonic phenomena and electronic structures.

Findings

Discovery of multiple plasmons in cI16 phase at 70 GPa

Reentrant metallic phase oC24 shows higher transparency

Predicted strong reflectivity anisotropy in oC40 and oC24

Abstract

The metal-semiconductor-metal transition in dense lithium is considered as an archetype of interplay between interstitial electron localization and delocalization induced by compression, which leads to exotic electride phases. In this work, the dynamic dielectric response and optical properties of the high-pressure electride phases of cI16, oC40 and oC24 in lithium spanning a wide pressure range from 40 to 200 GPa by first-principles calculations are reported. Both interband and intraband contribution to the dielectric function are deliberately treated with the linear response theory. One intraband and two interband plasmons in cI16 at 70 GPa induced by a structural distortion at 2.1, 4.1, and 7.7 eV are discovered, which make the reflectivity of this weak metallic phase abnormally lower than the insulating phase oC40 at the corresponding frequencies. More strikingly, oC24 as a reentrant metallic phase with higher conductivity becomes more transparent than oC40 in infrared and visible light range due to its unique electronic structure around Fermi surface. An intriguing reflectivity anisotropy in both oC40 and oC24 is predicted, with the former being strong enough for experimental detection within the spectrum up to 10 eV. The important role of interstitial localized electrons is highlighted, revealing diversity and rich physics in electrides.