Electronic topological transitions and vibrational properties of A-15 type X3Y (X= V, Cr and Mo; Y= Os, Ir and Pt) compounds: A first-principles study

Abstract

Ab-initio studies of A-15 type X3Y (X = V, Cr and Mo; Y= Os, Ir and Pt) compounds are presented at ambient and high pressures. All the studied compounds satisfy the mechanical stability criteria and are also dynamically stable as evidenced from the positive phonon dispersion curves. Camels back type band structure features are observed at Fermi level in some of the investigated compounds. Electronic topological transitions (ETTs) are the main highlights in all the compounds under pressure at different compressed volumes. The electron-phonon coupling constants λ are calculated on the basis of the Eliashberg theory for the Mo3Y (Y= Os, Ir and Pt) series that, according to the experiments, have the largest transition temperature among the studied compounds. Mo3Os superconductivity is fully understood on the basis of the Eliashberg theory of the phonon-mediated electron pairing and the experimental Tc is recovered using the well known Mc Millan formula. On the contrary, for the other two compounds of the same series Mo3Y (Ir and Pt) the calculated mass enhancement parameters show an unexpected behavior and for Mo3Ir, the experimental transition temperature values cannot be easily recovered through the Mc Millan formula.