Plasmons in Sodium under Pressure: Increasing Departure from Nearly-Free-Electron Behavior

TL;DR

This study measures how plasmon energies in sodium change under high pressure, revealing increasing deviations from free-electron behavior due to enhanced electron-ion interactions, supported by first-principles calculations.

Contribution

It provides the first detailed pressure-dependent plasmon measurements in sodium and links deviations to electronic structure changes rather than exchange-correlation effects.

Findings

Plasmon energies deviate more from free-electron predictions with pressure.

First-principles calculations attribute deviations to increased electron-ion interactions.

Additional measurements for potassium and rubidium are briefly discussed.

Abstract

We have measured plasmon energies in Na under high pressure up to 43 GPa using inelastic x-ray scattering (IXS). The momentum-resolved results show clear deviations, growing with increasing pressure, from the predictions for a nearly-free electron metal. Plasmon energy calculations based on first-principles electronic band structures and a quasi-classical plasmon model allow us to identify a pressure-induced increase in the electron-ion interaction and associated changes in the electronic band structure as the origin of these deviations, rather than effects of exchange and correlation. Additional IXS results obtained for K and Rb are addressed briefly.