Understanding the complex phase diagram of uranium: the role of electron-phonon coupling

TL;DR

This study investigates how pressure affects phonon behavior and electron-phonon interactions in uranium, revealing insights into its phase diagram, charge-density wave, and superconductivity through experimental and theoretical analysis.

Contribution

It provides the first detailed experimental data on phonon dispersion under pressure and demonstrates the pressure-dependent electron-phonon coupling in uranium.

Findings

Phonon energies increase rapidly with pressure up to 20 GPa.

Electron-phonon coupling varies strongly with pressure and momentum.

Fermi-surface nesting remains surprisingly pressure-independent.

Abstract

We report an experimental determination of the dispersion of the soft phonon mode along [1,0,0] in uranium as a function of pressure. The energies of these phonons increase rapidly, with conventional behavior found by 20 GPa, as predicted by recent theory. New calculations demonstrate the strong pressure (and momentum) dependence of the electron-phonon coupling, whereas the Fermi-surface nesting is surprisingly independent of pressure. This allows a full understanding of the complex phase diagram of uranium, and the interplay between the charge-density wave and superconductivity.