Electron-phonon superconductivity in $A$Pt$_3$P compounds: from weak to strong coupling

TL;DR

This study uses first-principles calculations and Migdal-Eliashberg theory to analyze electron-phonon superconductivity in $A$Pt$_3$P compounds, revealing a transition from weak to strong coupling and clarifying their superconducting nature.

Contribution

It provides a comprehensive first-principles analysis of $A$Pt$_3$P superconductors, excluding charge-density wave scenarios and exploring the effects of structure and spin-orbit coupling.

Findings

Superconductivity is well described by conventional s-wave pairing.

The pairing strength increases from La to Ca and Sr.

Spin-orbit coupling has a marginal effect on superconductivity.

Abstract

We study the newly discovered Pt phosphides $A$Pt$_3$P ($A$=Sr, Ca, La) [ T. Takayama et al. Phys. Rev. Lett. 108, 237001 (2012)] using first-principles calculations and Migdal-Eliashberg theory. Given the remarkable agreement with the experiment, we exclude the charge-density wave scenario proposed by previous first-principles calculations, and give conclusive answers concerning the superconducting state in these materials. The pairing increases from La to Ca and Sr due to changes in the electron-phonon matrix elements and low-frequency phonons. Although we find that all three compounds are well described by conventional s-wave superconductivity and spin-orbit coupling of Pt plays a marginal role, we show that it could be possible to tune the structure from centrosymmetric to noncentrosymmetric opening new perspectives towards the understanding of unconventional superconductivity.