Spin and charge susceptibilities of the two-orbital model within the cluster perturbation theory for Fe-based materials

TL;DR

This paper employs cluster perturbation theory combined with RPA to analyze spin and charge susceptibilities in a two-orbital model of iron pnictides, confirming the validity of simplified approaches for weak interactions.

Contribution

It introduces a combined cluster perturbation theory and RPA method to study susceptibilities in a multiorbital model of Fe-based materials, validating these methods for weak interactions.

Findings

RPA and rigid band approximation are suitable for U ≤ 2

Cluster perturbation theory effectively captures band structure and susceptibilities

Weak interactions do not significantly alter the model's predictions

Abstract

Cluster perturbation theory is used to calculate band structure, spectral functions, Fermi surface, and spin and charge susceptibilities for the two-orbital model of iron pnictides with the on-site multiorbital Hubbard interactions. Susceptibilities are calculated within the approximation combining the cluster perturbation theory for the self-energy corrections and the random-phase approximation (RPA) for the vertex renormalizations. Calculations for the small values of Hubbard repulsion $U \leq 2$ confirm that the rigid band approximation and RPA for the spin and charge susceptibilities are suitable approaches for the case of weak interactions.