Energy of bond defects in quantum spin chains obtained from local approximations and from exact diagonalization

TL;DR

This paper investigates how bond defects affect the ground-state energy of antiferromagnetic spin chains using both exact numerical methods and a new local-bond approximation, which improves upon mean-field results with minimal additional computation.

Contribution

The paper introduces a local-bond approximation for estimating energies in spin chains with defects, enhancing accuracy over mean-field methods without significant computational cost.

Findings

Local-bond approximation significantly improves energy estimates.

Numerical diagonalization confirms the accuracy of the approximation.

Bond defects influence ground-state energies in predictable ways.

Abstract

We study the influence of ferromagnetic and antiferromagnetic bond defects on the ground-state energy of antiferromagnetic spin chains. In the absence of translational invariance, the energy spectrum of the full Hamiltonian is obtained numerically, by an iterative modification of the power algorithm. In parallel, approximate analytical energies are obtained from a local-bond approximation, proposed here. This approximation results in significant improvement upon the mean-field approximation, at negligible extra computational effort.