Neutron and ARPES Constraints on the Couplings of the Multiorbital Hubbard Model for the Pnictides

TL;DR

This paper uses neutron scattering and ARPES data to constrain the realistic parameter ranges of multiorbital Hubbard models for Fe-pnictides, and explores pairing tendencies indicating nodal superconductivity.

Contribution

It provides phase diagrams for multiorbital Hubbard models with realistic parameters and investigates pairing channels using RPA, linking theory with experimental observations.

Findings

Realistic Hubbard parameters are constrained by experimental data.

Nodal spin-singlet pairing dominates in realistic regimes.

Multiple competing pairing states are identified.

Abstract

The results of neutron scattering and angle-resolved photoemission experiments for the Fe-pnictide parent compounds, and their metallic nature, are shown to impose severe constraints on the range of values that can be considered "realistic" for the intraorbital Hubbard repulsion U and Hund coupling J in multiorbital Hubbard models treated in the mean-field approximation. Phase diagrams for three- and five-orbital models are here provided, and the physically realistic regime of couplings is highlighted, to guide future theoretical work into the proper region of parameters of Hubbard models. In addition, using the random phase approximation, the pairing tendencies in these realistic coupling regions are investigated. It is shown that the dominant spin-singlet pairing channels in these coupling regimes correspond to nodal superconductivity, with strong competition between several states that belong to different irreducible representations. This is compatible with experimental bulk measurements that have reported the existence of nodes in several Fe-pnictide compounds.