Spin dynamics of hole doped Y2BaNiO5

TL;DR

This paper develops an effective Hamiltonian for hole-doped Y2BaNiO5, revealing low-energy spin excitations within the Haldane gap through numerical analysis, aligning with experimental observations.

Contribution

It introduces a detailed multiband Hamiltonian and derives an effective model for doped Y2BaNiO5, capturing complex spin-charge interactions beyond simple models.

Findings

Identification of low-energy excitations inside the Haldane gap.

Effective Hamiltonian describing O fermions interacting with Ni spins.

Results consistent with experimental data on doped Y2BaNiO5.

Abstract

Starting from a multiband Hamiltonian containing the relevant Ni and O orbitals, we derive an effective Hamiltonian $H_{eff}$ for the low energy physics of doped Y$_{2}$BaNiO$_{5}.$ For hole doping, $H_{eff}$ describes O fermions interacting with S=1 Ni spins in a chain, and cannot be further reduced to a simple one-band model. Using numerical techniques, we obtain a dynamical spin structure factor with weight inside the Haldane gap. The nature of these low-energy excitations is identified and the emerging physical picture is consistent with most of the experimental information in Y% $_{2-x}$Ca$_{x}$BaNiO$_{5}$