$XXZ$ model as effective Hamiltonian for generalized Hubbard models with broken $\eta$-symmetry

TL;DR

This paper explores how breaking $ta$-symmetry in generalized Hubbard models affects their equivalence to the XXZ spin chain and the resulting impact on superconducting order, revealing the disappearance of off-diagonal long-range order.

Contribution

It demonstrates how perturbations breaking $ta$-symmetry influence the ground state and superconducting properties of the model, extending understanding of symmetry effects in correlated systems.

Findings

Breaking $ta$-symmetry destroys off-diagonal long-range order.

The ground state forms a large bound state of magnons.

Perturbations lead to the loss of superconducting phase coherence.

Abstract

We consider the limit of strong Coulomb attraction for generalized Hubbard models with $\eta$-symmetry. In this limit these models are equivalent to the ferromagnetic spin-1/2 Heisenberg quantum spin chain. In order to study the behaviour of the superconducting phase in the electronic model under perturbations which break the $\eta$-symmetry we investigate the ground state of the ferromagnetic non-critical $XXZ$-chain in the sector with fixed magnetization. It turns out to be a large bound state of $N$ magnons. We find that the perturbations considered here lead to the disappearance of the off-diagonal longe-range order.