Superconductivity and Lattice Instability in Compressed Lithium from Fermi Surface Hot Spots

TL;DR

This paper explains the high superconducting temperature in compressed lithium as resulting from critical electron-phonon interactions at Fermi surface hot spots, with first-principles calculations revealing phonon instabilities and anharmonic stabilization.

Contribution

It demonstrates the link between Fermi surface hot spots, phonon instabilities, and superconductivity in lithium under pressure using first-principles calculations.

Findings

Superconductivity in lithium arises from electron-phonon coupling at Fermi surface hot spots.

Phonon instabilities occur at 25 GPa, indicating anharmonic stabilization.

The highest T_c is associated with critical electron-phonon interactions along specific phonon branches.

Abstract

The highest superconducting temperature T$_c$ observed in any elemental metal (Li with T$_c$ ~ 20 K at pressure P ~ 40 GPa) is shown to arise from critical (formally divergent) electron-phonon coupling to the transverse T$_1$ phonon branch along intersections of Kohn anomaly surfaces with the Fermi surface. First principles linear response calculations of the phonon spectrum and spectral function $\alpha^2 F(\omega)$ reveal (harmonic) instability already at 25 GPa. Our results imply that the fcc phase is anharmonically stabilized in the 25-38 GPa range.