Parametrized canonical transformation for the Hubbard-model at arbitrary interaction strength

TL;DR

This paper introduces a parametrized canonical transformation for the Hubbard model that improves convergence properties, enabling accurate descriptions of the ground state at arbitrary interaction strengths, including weak coupling regimes.

Contribution

The authors develop a modified canonical transformation that yields alternative Hubbard-like models with better convergence, extending the applicability to lower interaction strengths.

Findings

Enhanced description of the half-filled ground state at $0<U ext{ to }1$

Improved convergence properties of the transformed models

Effective analysis of observables for different variational wave-functions

Abstract

The $t-J$ and Heisenberg models are truncated expansions of a canonically transformed Hubbard model coinciding with it at $U\to \infty$. We show that a modified canonical transformation applied to the Hubbard model leads to alternative models of the same form, but whose convergence properties with respect to the expansion are more favourable, resulting in a good description of the half-filled ground state even at $0<U\leq1$. We investigate the transformed Hamiltonian and observables for metallic and insulating variational wave-functions.