Disorder is important in the study of quantum spin liquids, but its role on the spin dynamics remains elusive. Here, we explore the disorder effect by investigating the magnetic-field dependence of the low-energy magnetic excitations in a triangular-lattice frustrated magnet YbZnGaO4 with inelastic neutron scattering. With an intermediate field of 2.5 T applied along the c-axis, the broad continuum at zero field becomes more smeared both in energy and momentum. With a field up to 10 T, which fully polarizes the magnetic moments, we observe clear spin-wave excitations with a gap of ∼1.4 meV comparable to the bandwidth. However, the spectra are significantly broadened. The excitation spectra both at zero and high fields can be reproduced by performing classical Monte Carlo simulations which take into account the disorder effect arising from the random site mixing of nonmagnetic Zn2+ and Ga3+ ions. These results elucidate the critical role of disorder in broadening the magnetic excitation spectra and mimicking the spin-liquid features in frustrated quantum magnets.
@article{arxiv.2202.05462,
title = {Disorder-induced broadening of the spin waves in a triangular-lattice quantum-spin-liquid candidate YbZnGaO$_4$},
author = {Zhen Ma and Zhao-Yang Dong and Jinghui Wang and Shuhan Zheng and Kejing Ran and Song Bao and Zhengwei Cai and Yanyan Shangguan and Wei Wang and M. Boehm and P. Steffens and L. -P. Regnault and Xiao Wang and Yixi Su and Shun-Li Yu and Jun-Ming Liu and Jian-Xin Li and Jinsheng Wen},
journal= {arXiv preprint arXiv:2202.05462},
year = {2022}
}