Origin of Strong Coupling in Lithium under Pressure

TL;DR

This study investigates the origin of high superconducting transition temperature in lithium under pressure by detailed phonon and electron-phonon interaction calculations, revealing contributions from multiple phonon modes.

Contribution

It provides a detailed, high-resolution analysis of phonon modes and electron-phonon interactions in lithium at 20 GPa, highlighting the importance of fine mesh calculations for accurate results.

Findings

High T_c in lithium is influenced by multiple phonon modes.

Finer mesh calculations are essential for converged electron-phonon spectral functions.

Both transverse and longitudinal phonon modes contribute to superconductivity.

Abstract

In an attempt to provide a clearer understanding of the impressive increase in T_c under pressure in elemental Li, linear response calculation of the phonon dispersion curves, electron-phonon matrix elements, phonon linewidths and mode lambda's have been carried out on a finer mesh (24^3 in the Brillouin zone) than done previously, for the volume corresponding to 20 GPa pressure. The result illustrates the great need for a fine mesh (even finer than this) for converged results of lambda and the spectral function alpha^2 F. Although the initial pressure-induced transverse T_1 phonon instability (in harmonic approximation) near the symmetry point K has dominated attention, the current results show that the high value of T_c gets strong contributions from elsewhere in the zone, particularly from the longitudinal mode along (100).