On-site Atractive Multiorbital Hamiltonian for $d$-Wave Superconductors

TL;DR

This paper introduces a two-orbital attractive Hamiltonian that models $d$-wave superconductivity in multiorbital systems, providing insights into high-temperature cuprate superconductors and extending the negative-$U$ Hubbard model framework.

Contribution

It presents a new two-orbital Hamiltonian with on-site attraction that develops $d$-wave superconductivity, supported by mean-field analysis and exact diagonalization, applicable to multiorbital high-$T_c$ materials.

Findings

The model exhibits $d$-wave pairing with nodes along the Brillouin zone diagonals.

Exact diagonalization confirms the emergence of $d$-wave superconductivity.

The model reproduces key properties of cuprate superconductors at specific orbital fillings.

Abstract

We introduce a two-orbital Hamiltonian on a square lattice that contains on-site attractive interactions involving the two $e_g$ orbitals. Via a canonical mean-field procedure similar to the one applied to the well-known negative-$U$ Hubbard model, it is shown that the new model develops $d$-wave ($B_{1g}$) superconductivity with nodes along the diagonal directions of the square Brillouin zone. This result is also supported by exact diagonalization of the model in a small cluster. The expectation is that this relatively simple attractive model could be used to address the properties of multiorbital $d$-wave superconductors in the same manner that the negative-$U$ Hubbard model is widely applied to the study of the properties of $s$-wave single-orbital superconductors. In particular, we show that by splitting the $e_g$ orbitals and working at three-quarters filling, such that the $x^2-y^2$ orbital dominates at the Fermi level but the $3z^2-r^2$ orbital contribution is nonzero, the $d$-wave pairing state found here phenomenologically reproduces several properties of the superconducting state of the high $T_c$ cuprates.