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

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.

High-pressure lithium as an elemental topological semimetal

“…The structural changes are coupled to counterintuitive modifications of its electronic properties, which cannot be explained by a theory based on the nearly-free-electron approximation. A number of exotic high pressure phenomena ensue, including a metal to semiconductor transition, reappearance of metallization, superconductivity, anomalous melting curve, and electride properties [2,6,7,10,[13][14][15][16][17][18][19].…”

All-electron product basis set: Application to plasmon anisotropy in simple metals

“…In particular, zone boundary collective states were identified in Al 52 and in Li and Na 53 . The relation between the underlying band structure and the energy loss function was analyzed for Al 45,54,55 and for alkali metals 40,41,[56][57][58][59] , also under pressure [60][61][62][63][64][65][66] . In cesium, the interband transitions were found to cause a negative plasmon dispersion 40,41 .…”

Anomalous thermophysical properties and electride transition in fcc potassium

“…Simultaneously, the absorption spectrum of Na-HPE is strongly anisotropic, i.e., sodium becomes optically transparent in one direction but reflective in the other ones [11]. Besides, the reflectivity of both solid and liquid alkali metals (mainly lithium [17] and potassium [18]) shows a slight dip across the electride transition region. Furthermore, it is found that the electron and phonon interaction in HPE state can give rise to an anomalous LA-TA splitting in the phonon 4 dispersion [19].…”