The susceptibility and excitation spectrum of (VO)$_2$P$_2$O$_7$ in ladder and dimer chain models

TL;DR

This paper investigates the magnetic susceptibility and excitation spectrum of (VO)$_2$P$_2$O$_7$ using ladder and dimer chain models, providing parameter estimates and predictions for energy gaps and dispersion relations.

Contribution

It offers a detailed numerical analysis of susceptibility in spin ladder and dimer chain models, fitting experimental data to determine interaction parameters and excitation gaps.

Findings

Estimated exchange interactions: J_perp=7.82 meV, J_parallel=7.76 meV

Predicted singlet-triplet gap: 3.9 meV

Dimer chain fit yields a gap of 4.9 meV

Abstract

We present numerical results for the magnetic susceptibility of a Heisenberg antiferromagnetic spin ladder, as a function of temperature and the spin-spin interaction strengths $J_\perp$ and $J_{||}$. These are contrasted with new bulk limit results for the dimer chain. A fit to the experimental susceptibility of the candidate spin-ladder compound vanadyl pyrophosphate, (VO)$_2$P$_2$O$_7$, gives the parameters $J_\perp = 7.82$ meV and $J_{||} = 7.76$ meV. With these values we predict a singlet-triplet energy gap of $E_{gap} = 3.9$ meV, and give a numerical estimate of the ladder triplet dispersion relation $\omega(k)$. In contrast, a fit to the dimer chain model leads to $J_1=11.11$ meV and $J_2=8.02$ meV, which predicts a gap of $E_{gap} = 4.9$ meV.