Spin correlations in the paramagnetic phase and ring exchange in lanthanum cuprate

TL;DR

This paper investigates spin correlations in lanthanum cuprate's paramagnetic phase using polarized neutron scattering, confirming quantum model predictions and providing experimental evidence for ring exchange interactions.

Contribution

It presents the first experimental evidence for ring exchange in lanthanum cuprate and validates quantum non-linear sigma model predictions for spin fluctuations.

Findings

Temperature dependence matches quantum non-linear sigma model

Evidence for ring exchange interactions

Quantitative agreement with theoretical predictions

Abstract

Spin correlations in the paramagnetic phase of lanthanum cuprate have been studied using polarized neutron scattering, with two important results. First, the temperature dependence of the characteristic energy scale of the fluctuations and the amplitude of the neutron structure factor are shown to be in quantitative agreement with the predictions of the quantum non-linear sigma model. Secondly, comparison of a high-temperature series expansion of the equal-time spin correlations with the diffuse neutron intensity provides definitive experimental evidence for ring exchange.