Properties of a two orbital model for oxypnictide superconductors: Magnetic order, B_2g spin-singlet pairing channel, and its nodal structure

Abstract

A two orbital model for the new Fe-based superconductors is studied using the Lanczos method as well as pairing mean-field approximations. Our main goals are (i) to provide a comprehensive analysis of this model using numerical techniques with focus on half-filling and on the state with two more electrons than half-filling and (ii) to investigate the nodal structure of the mean-field superconducting state and compare the results with angle-resolved photoemission data. In particular, we provide evidence that at half-filling spin 'stripes', as observed experimentally, dominate over competing states. Depending on parameters, the state with two more electrons added to half filling is either triplet or singlet. Since experiments suggest spin singlet pairs, our focus is on this state. Under rotation, it transforms as the B_2g representation of the D_4h group. We also show that the s+/- pairing operator transforms as A_1g and becomes dominant only in an unphysical regime of the model where the undoped state is an insulator. For robust values of the effective electronic attraction producing the Cooper pairs, assumption compatible with recent angle-resolved photoemission (ARPES) results that suggesting small Cooper-pair size, the nodes of the two-orbital model are found to be located only at the electron pockets. Since recent ARPES efforts have searched for nodes at the hole pockets or only in a few directions at the electron pockets, our results for the nodal distribution may help to guide future experiments. More in general, the investigations reported here aim to establish several of the properties of the two orbital model. Only a detailed comparison with experiments will clarify how far this simple model present a valid description of the Fe pnictides.

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• Low-energy microscopic models for iron-based superconductors: a review
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• U(1) Slave-spin theory and its application to Mott transition in a multi-orbital model for iron pnictides
• Neutron and ARPES Constraints on the Couplings of the Multiorbital Hubbard Model for the Pnictides
• Magnetic States of the Two-Leg Ladder Alkali Metal Iron Selenides $A$Fe${}_2$Se${}_3$
• Orbital-weight redistribution triggered by spin order in the pnictides
• Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictides
• Tight binding model for iron pnictides
• On interband pairing in multiorbital systems
• Orbital selectivity in electron correlations and superconducting pairing of iron-based superconductors
• Magnetic order in orbital models of the iron pnictides
• Vertical loop nodes in iron-based superconductors
• Screening in a two-band model for superconducting infinite-layer nickelate
• A Two-band Model for p-wave Superconductivity
• Spin Resonances in Iron-Selenide High-Tc Superconductors by Proximity to Hidden Spin Density Wave
• Superconductivity by Hidden Spin Fluctuations in Electron-Doped Iron Selenide
• Anisotropic magnetic excitations of a frustrated bilinear-biquadratic spin model -- Implications for spin waves of detwinned iron pnictides
• Constraints Imposed by Symmetry on Pairing Operators for the Pnictides
• Ferroelectricity-induced multiorbital odd-frequency superconductivity in SrTiO${}_3$
• Resource-optimized fault-tolerant simulation of the Fermi-Hubbard model and high-temperature superconductor models
• Comment on "Nonmagnetic Impurity Resonances as a Signature of Sign-Reversal Pairing in Fe-As-Based Superconductors"
• Momentum distribution and non-Fermi liquid behaviour in low-doped two-orbital model: finite-size cluster quantum Monte Carlo approach
• Enhancing long-range order in disordered two-band s-wave superconductors