Study of phase diagram and superconducting states in LaFeAsO$_{1-x}$H$_x$ based on the multiorbital extended Hubbard model

TL;DR

This study investigates the complex magnetic and superconducting phase diagram of LaFeAsO$_{1-x}$H$_x$ using a multiorbital Hubbard model, revealing strong orbital and spin fluctuations that influence superconductivity.

Contribution

It provides a detailed analysis beyond the rigid band approximation, highlighting the role of orbital and spin fluctuations and quadrupole interactions in the phase diagram.

Findings

Orbital and spin fluctuations develop strongly at both ends of doping range.

Quadrupole interactions are enhanced by Coulomb vertex corrections.

The results explain the double-dome superconducting phase.

Abstract

To understand the recently established unique magnetic and superconducting phase diagram of LaFeAsO$_{1-x}$H$_x$, we analyze the realistic multiorbital tight-binding model for $x=0 \sim 0.4$ beyond the rigid band approximation. Both the spin and orbital susceptibilities are calculated in the presence of the Coulomb and charge quadrupole interactions. It is found that both orbital and spin fluctuations strongly develop at both $x \sim 0$ and 0.4, due to the strong violation of the rigid band picture in LaFeAsO$_{1-x}$H$_x$. Based on this result, we discuss the experimental phase diagram, especially the double-dome superconducting phase. Moreover, we show that the quadrupole interaction is effectively produced by the vertex correction due to Coulomb interaction, resulting in the mutual development of spin and orbital fluctuations.