Novel Electronic Structures of Ru-Pnictides Ru$Pn$ ($Pn$ = P, As, Sb)

TL;DR

This study uses density functional theory to explore the electronic structures of Ru-pnictides RuP, RuAs, and RuSb, revealing flat bands near the Fermi level that are linked to phase transitions and superconductivity.

Contribution

It uncovers the origin of flat bands in RuP and RuAs and explains their role in phase transitions and superconductivity, providing new insights into their electronic states.

Findings

Flat bands appear at the Fermi level in RuP and RuAs.

Rh doping shifts the Fermi level above the flat bands.

RuSb's band structure resembles doped RuP and RuAs, explaining superconductivity.

Abstract

Density-functional-theory-based electronic structure calculations are made to consider the novel electronic states of Ru-pnictides RuP and RuAs where the intriguing phase transitions and superconductivity under doping of Rh have been reported. We find that there appear nearly degenerate flat bands just at the Fermi level in the high-temperature metallic phase of RuP and RuAs; the flat-band states come mainly from the $4d_{xy}$ orbitals of Ru ions and the Rh doping shifts the Fermi level just above the flat bands. The splitting of the flat bands caused by their electronic instability may then be responsible for the observed phase transition to the nonmagnetic insulating phase at low temperatures. We also find that the band structure calculated for RuSb resembles that of the doped RuP and RuAs, which is consistent with experiment where superconductivity occurs in RuSb without Rh doping.