Charge Density Wave Instability and Soft Phonon in $A$Pt$_3$P ($A$=Ca, Sr, and La)

TL;DR

This study uses first-principles calculations to explore electronic and phonon properties of $A$Pt$_3$P superconductors, revealing a unique charge-density-wave instability in SrPt$_3$P that influences its superconducting behavior.

Contribution

It uncovers a weak charge-density-wave instability in SrPt$_3$P unrelated to Fermi-surface nesting, and shows how pressure suppresses this instability and affects superconductivity.

Findings

SrPt$_3$P exhibits a weak CDW instability not linked to Fermi-surface nesting.

External pressure suppresses the CDW instability and reduces $T_c$.

Superconductivity in SrPt$_3$P is enhanced by CDW fluctuations.

Abstract

The electronic and phonon properties of the platinum pnictide superconductors $A$Pt$_3$P ($A$=Ca, Sr, and La) were studied using first-principles calculations. The spin-orbit coupling effect is significant in LaPt$_3$P but negligible in CaPt$_3$P and SrPt$_3$P, although they all share the same anti-pevroskite structure. Moreover, SrPt$_3$P has been demonstrated to exhibit an unexpected weak charge-density-wave(CDW) instability which is neither simply related to the Fermi-surface nesting nor to the momentum-dependent electron-phonon coupling alone. The instability is absent in CaPt$_3$P and can be quickly suppressed by the external pressure, accompanied with gradual decreases in the phonon softening and BCS $T_c$. Our results suggest SrPt$_3$P as a rare example where superconductivity is enhanced by the CDW fluctuations.