Symmetry breaking and restoring under high pressure: the amazing behaviour of the "simple" alkali metals

TL;DR

This paper explores how alkali metals undergo multiple phase transitions between symmetric and dimerized structures under high pressure, driven by Friedel oscillations, with predictions of eventual phase restoration at extreme densities.

Contribution

It introduces a model explaining pressure-induced phase oscillations in alkali metals due to Friedel oscillations, predicting phase restoration at high densities.

Findings

Alkali metals oscillate between symmetric and dimerized phases under pressure.

Friedel oscillations influence phase stability in alkali metals.

Symmetric phase is predicted to reappear at very high densities.

Abstract

We argue that an ionic lattice surrounded by a Fermi liquid changes phase several times under pressure, oscillating between the symmetric phase and a low-symmetry dimerized structure, as a consequence of Friedel oscillations in the pair potential. Phase oscillations explain the tendency towards dimerization which has been recently reported for the light alkali metals under high pressure. Moreover, a restoring of the symmetric phase is predicted for such elements at an even higher density.