Bond-versus-site doping models for off-chain-doped Haldane-gap system Y$_2$ Ba Ni O$_5$

TL;DR

This study compares two models of off-chain doping in the Haldane-gap system Y$_2$ Ba Ni O$_5$, revealing differences in impurity energy levels and low-energy excitations that can be experimentally observed.

Contribution

It introduces and analyzes ferromagnetic bond doping and antiferromagnetic site doping models for Y$_2$ Ba Ni O$_5$ using DMRG, highlighting their distinct impurity effects.

Findings

Localized state thresholds identified for both models

Differences in low-energy excitations between models

Potential experimental detection of model-specific effects

Abstract

Using the density matrix renormalization-group technique, we calculate the impurity energy levels for two different effective models of off-chain doping for quasi-one-dimensional Heisenberg chain compound Y$_2$ Ba Ni O$_5$: ferromagnetic bond doping and antiferromagnetic site spin-1/2 doping. Thresholds of the impurity strength for the appearance of localized states are found for both models. However, the ground-state and low-energy excitations for weak impurity strength are different for these two models and the difference can be detected by experiments.