Eur. Phys. J. Plus (2024) 139: 841
https://doi.org/10.1140/epjp/s13360-024-05653-7

Regular Article

Interplay between charge ordering and superconducting correlations in the extended Hubbard model

Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01, Košice, Slovakia

^a farky@saske.sk

Received: 26 March 2024
Accepted: 12 September 2024
Published online: 21 September 2024

Abstract

We examine effects of charge ordering on superconducting correlations in the extended Hubbard model with Falicov-Kimball coupling in two dimensions. Charge orderings are generated by f-electron distributions on the localized f orbitals, which act as an internal potential for itinerant d electrons moving in the Hubbard d band. For the small finite cluster of $L=4\times 4$ sites the model is studied exactly over the complete set of f-electron distributions, while for larger clusters the projector Quantum-Monte-Carlo method and the reduced set of f-electron distributions (the periodic, phase separated and phase segregated configurations) is used. It is found that the enhancement of superconducting correlations in the d-wave channel depends strongly on the type of f-electron ordering and changes significantly with f and d electron concentration ($n_f$,$n_d$) as well as with interband Coulomb interaction $U_{\mathit{fd}}$. In particular, it is found that for small values of $U_{\mathit{fd}}$ and $n_d$ the superconducting correlations are the most significantly enhanced for segregated configurations (all f-electrons clump together), for all f-electron concentrations, while for higher d-band fillings axial stripes (bands) with f-electron concentrations $n_f\sim 0.5$ yield the largest enhancement of superconducting correlations. The region of axial striped phases is systematically reduced with increasing $U_{\mathit{fd}}$ and for sufficiently large $U_{\mathit{fd}}$ ($U_{\mathit{fd}}\sim 2$) it persists only in the region of small $n_f$ and $n_d$ values.