The coexistence of charge density wave and superconductivity in Pt-based layered superconductors : SrPt$_2$As$_2$ and LaPt$_2$Si$_2$

TL;DR

This study uses ab initio calculations to explore how charge density waves and superconductivity coexist in SrPt$_2$As$_2$ and LaPt$_2$Si$_2$, revealing different mechanisms driving CDW formation in these layered superconductors.

Contribution

It demonstrates the distinct mechanisms behind CDW instabilities in SrPt$_2$As$_2$ and LaPt$_2$Si$_2$, and confirms their coexistence with superconductivity through phonon calculations.

Findings

CDW driven by Fermi surface nesting in SrPt$_2$As$_2$

CDW driven by saddle point scattering in LaPt$_2$Si$_2$

Coexistence of CDW and superconductivity in both materials

Abstract

The intriguing coexistence of the charge density wave (CDW) and superconductivity in SrPt$_2$As$_2$ and LaPt$_2$Si$_2$ has been investigated based on the {\it ab initio} density functional theory band structure and phonon calculations. We have found that the local split distortions Pt atoms in the [As-Pt-As] layers play an essential role in driving the five-fold supercell CDW instability as well as the phonon softening instability in SrPt$_2$As$_2$. By contrast, the CDW and phonon softening instabilities in LaPt$_2$Si$_2$ occur without split distortions of Pt atoms, indicating that the driving mechanisms of the CDW in SrPt$_2$As$_2$ and LaPt$_2$Si$_2$ are different. We have found that the CDW instability for the former arises from the Fermi surface nesting, while, for the latter, from the saddle point scattering. The phonon calculations, however, suggest that the CDW and the superconductivity coexist in [{\it X}-Pt-{\it X}] layers ({\it X} = As or Si) for both cases.