Quantum fluctuations in low-dimensional systems and near quantum phase transitions have significant influences on material properties. Yet, it is difficult to experimentally gauge the strength and importance of quantum fluctuations. Here we provide a resonant inelastic x-ray scattering study of magnon excitations in Mott insulating cuprates. From the thin film of SrCuO2, single- and bi-magnon dispersions are derived. Using an effective Heisenberg Hamiltonian generated from the Hubbard model, we show that the single-magnon dispersion is only described satisfactorily when including significant quantum corrections stemming from magnon-magnon interactions. Comparative results on La2CuO4 indicate that quantum fluctuations are much stronger in SrCuO2 suggesting closer proximity to a magnetic quantum critical point. Monte Carlo calculations reveal that other magnetic orders may compete with the antiferromagnetic N\'eel order as the ground state. Our results indicate that SrCuO2 - due to strong quantum fluctuations - is a unique starting point for the exploration of novel magnetic ground states.
@article{arxiv.2311.16553,
title = {Magnon interactions in a moderately correlated Mott insulator},
author = {Qisi Wang and S. Mustafi and E. Fogh and N. Astrakhantsev and Z. He and I. Biało and Ying Chan and L. Martinelli and M. Horio and O. Ivashko and N. E. Shaik and K. von Arx and Y. Sassa and E. Paris and M. H. Fischer and Y. Tseng and N. B. Christensen and A. Galdi and D. G. Schlom and K. M. Shen and T. Schmitt and H. M. Rønnow and J. Chang},
journal= {arXiv preprint arXiv:2311.16553},
year = {2024}
}