Effect of local charge fluctuations on spin physics in the Neel state of La$_2$CuO$_4$

TL;DR

This paper investigates how local charge fluctuations influence spin dynamics in La$_2$CuO$_4$, deriving an effective model that accurately fits experimental magnon dispersion and reveals renormalized magnetic properties.

Contribution

It introduces a Hubbard model-based effective spin model incorporating charge fluctuations, providing improved fits to experimental data and new insights into magnetic property renormalization.

Findings

Accurate magnon dispersion fit with Hubbard parameters U≈2.34 eV, t≈360 meV.

Renormalized staggered magnetization and local moments due to charge fluctuations.

Predicted continuum weight and secondary peaks in dynamical structure factor.

Abstract

We explore the effect of local charge fluctuations on the spin response of a Mott insulator by deriving an effective spin model, and studying it using Schwinger boson mean field theory. Applying this to La$_2$CuO$_4$, we show that an accurate fit to the magnon dispersion relation, measured by Coldea {\em et al.} [Phys. Rev. Lett. {\bf 86}, 5377 (2001)] is obtained with Hubbard model parameters $U \approx 2.34 eV$, and $t \approx 360 meV$. These parameters lead to estimates of the staggered magnetization ($m_s \approx 0.25$), spin wave velocity ($c\approx 800 meV$-\AA), and spin stiffness ($\rho_s \approx 24 meV$). In particular the staggered moment as well as the effective local moment are renormalized to smaller values compared to the Heisenberg model due to local charge fluctuations in the Hubbard model. The dynamical structure factor shows considerable weight in the continuum along the zone boundary as well as secondary peaks that may be observed in high resolution neutron scattering experiments.