Enhancement of the d-wave pairing correlations by charge and spin ordering in the spin-one-half Falicov-Kimball model with Hund and Hubbard~coupling

TL;DR

This study uses Quantum Monte Carlo simulations to explore how charge and spin interactions influence ordering and d-wave superconductivity in a complex electron model, revealing that certain charge/spin arrangements enhance pairing correlations.

Contribution

It demonstrates that interband Coulomb interactions and magnetic ordering significantly affect charge/spin phases and d-wave pairing in the Falicov-Kimball model with Hund and Hubbard couplings.

Findings

Charge/spin interactions stabilize specific ordering phases.

d-wave correlations are enhanced in striped and phase-separated states.

Antiferromagnetic order within chains boosts pairing, ferromagnetic order suppresses it.

Abstract

Projector Quantum-Monte-Carlo Method is used to examine effects of the spin-independent $U_{fd}$ as well as spin-dependent $J_z$ Coulomb interaction between the localized $f$ and itinerant $d$ electrons on the stability of various types of charge/spin ordering and superconducting correlations in the spin-one-half Falicov-Kimball model with Hund and Hubbard coupling. The model is studied for a wide range of $f$ and $d$-electron concentrations and it is found that the interband interactions $U_{fd}$ and $J_z$ stabilize three basic types of charge/spin ordering, and namely, (i) the axial striped phases, (ii) the regular $n$-molecular phases and (iii) the phase separated states. It is shown that the d-wave pairing correlations are enhanced within the axial striped and phase separated states, but not in the regular phases. Moreover, it was found that the antiferromagnetic spin arrangement within the chains further enhances the d-wave paring correlations, while the ferromagnetic one has a fully opposite effect.