Ab initio investigations of phonon anomalies and superconductivity in the rock-salt YS

Abstract

The phonon spectrum, phonon linewidths and electron–phonon coupling parameter for YS have been calculated by using a first-principles scheme, based on the application of the plane-wave pseudopotential method, density functional theory, and a linear response technique. Our phonon results confirm the presence of anomalous features in the neutron-scattering spectrum for the longitudinal acoustic branch. It is shown that the electronic d-state effects are primarily responsible for the anomalous phonon behaviour. The calculated values of phonon linewidths along various symmetry directions are presented and discussed. The longitudinal acoustic phonon linewidth shows a maximum at the zone boundary L where the branch exhibits a pronounced dip. The calculated electron–phonon coupling parameter, λ = 0.52, compares very well with a previous empirical value of 0.56.

Acknowledgements

This work was supported by the Scientific and Technical Research Council of Turkey (TUBİTAK) and the Engineering and Physical Sciences Research Council of United Kingdom (EPSRC).