First-principles study of the electronic structure of CaKRu$_4$P$_4$

TL;DR

This study uses first-principles calculations to explore the electronic structure of CaKRu$_4$P$_4$, revealing its potential as a superconductor and a platform for topological physics, with pressure tuning its properties.

Contribution

It provides the first detailed electronic structure analysis of CaKRu$_4$P$_4$, highlighting its differences from iron-based superconductors and its potential for superconductivity and topological states.

Findings

CaKRu$_4$P$_4$ lacks hole carriers without spin-orbit interaction.

No long-range magnetic order in the ground state.

Pressure induces topological Dirac fermions and makes the electronic structure similar to 122-type compounds.

Abstract

The recent discovery and studies of 1144-phase compounds, e.g., CaKFe$_4$As$_4$, have attracted significant research interest. In this paper, based on the first-principles density functional calculations, we present a systematic study on the electronic structure of the recently synthetized 1144-type quaternary compound CaKRu$_4$P$_4$. We find that the Ru-based 1144-type compound possesses a different electronic structure from that of iron-based superconductors, even though they share very similar crystallographic structures. In CaKRu$_4$P$_4$, there is no hole-type carrier if spin-orbit interaction is not considered. And a long-range magnetic order is absent in its ground state. With the application of pressure, the electronic structure of CaKRu$_4$P$_4$ becomes similar to those of the ternary 122-type compounds LaRu$_2$P$_2$ and LaRu$_2$As$_2$. CaKRu$_4$P$_4$ is very likely to be a phonon-mediated medium coupled BCS superconductor. Furthermore, type-I and type-II Dirac fermions can be created and regulated in this system with pressure. The quaternary compound CaKRu$_4$P$_4$ therefore has a potential to be an attractive platform for the study of topological physics and superconductivity.