Spin Dynamics of Hole Doped ${\rm Y_{2-x} Ca_x Ba Ni O_5}$

TL;DR

This paper develops a theoretical model for hole-doped ${\rm Y_{2-x} Ca_x Ba Ni O_5}$, capturing its spin dynamics and spectral features, and compares predictions with neutron scattering experiments.

Contribution

A multiband to one-band model derivation for the compound, revealing hole propagation on a spin chain and predicting low-energy states with S=3/2.

Findings

Spectral weight observed in the Haldane gap matches neutron scattering data.

Low energy S=3/2 states are predicted by the model.

Several experimental predictions are proposed for validation.

Abstract

We propose an electronic model for the recently discovered hole doped compound ${\rm Y_{2-x} Ca_x Ba Ni O_5 }$. From a multiband Hamiltonian with oxygen and nickel orbitals, a one band model is derived. Holes are described using Zhang-Rice-like S=1/2 states at the nickels propagating on a S=1 spin chain. Using numerical techniques to calculate the dynamical spin structure factor ${\rm S(q,\omega)}$ in a realistic regime of couplings, spectral weight in the Haldane gap is observed in agreement with neutron scattering data. Low energy states with S=3/2 appear in the model. Several predictions are made to test these ideas.