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

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 $\hat{I}{\pm }^{2}F(\ddot{I}‰)$ reveal (harmonic) instability already at 25 GPa. Our results imply that the fcc phase is anharmonically stabilized in the 25-38 GPa range.

4 pages, 3 embedded figures