Superconductivity and lattice instability in face-centered cubic lanthanum under high pressure

The lattice dynamics and superconductivity of face-centered cubic (fcc) La under pressure are extensively studied using the linear-response methods within the framework of density-functional theory. A pressure-induced softening transverse acoustic (TA) phonon mode at the L point of the Brillouin zone is identified and the phonon softening pressure was predicted to be similar to 4.92 GPa, which coincides with the experimentally observed second-order phase transition pressure of similar to 5.3 GPa from fcc to distorted fcc. Moreover, no elastic instability is found under compression. Analysis of the calculated results suggests that the TA phonon instability is the driving force for this second-order phase transition. Furthermore, the current electron-phonon coupling (EPC) calculations suggest that the experimental observation of elevated superconducting transition temperature T-c with pressure is from the increased EPC strength and the softening TA phonon.