Quantum spin systems exhibit an enormous range of collective excitations, but their spin waves, gapped triplons, fractional spinons, or yet other modes are generally held to be mutually exclusive. Here we show by neutron spectroscopy on SeCuO3 that magnons, triplons, and spinons are present simultaneously. We demonstrate that this is a consequence of a structure consisting of two coupled subsystems and identify all the interactions of a minimal magnetic model. Our results serve qualitatively to open the field of multi-excitation spin systems and quantitatively to constrain the complete theoretical description of one member of this class of materials.
@article{arxiv.2007.02972,
title = {Triplons, Magnons, and Spinons in a Single Quantum Spin System: SeCuO3},
author = {Luc Testa and Vinko Surija and Krunoslav Prsa and Paul Steffens and Martin Boehm and Philippe Bourges and Helmut Berger and Bruce Normand and Henrik Ronnow and Ivica Zivkovic},
journal= {arXiv preprint arXiv:2007.02972},
year = {2021}
}