Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Stable composite objects (e.g. hadrons, nuclei, atoms, molecules, and superconducting pairs) formed by attractive forces are ubiquitous in nature. In contrast, composite objects stabilized via repulsive forces were long thought to be theoretical constructions due to their fragility in naturally occurring systems. Surprisingly, the formation of bound atom pairs by strong repulsive interactions has been demonstrated experimentally in optical lattices1. Despite this success, repulsively bound particle pairs were believed to have no analogue in condensed matter due to strong decay channels. Here, we present spectroscopic signatures of repulsively bound three-magnon states and bound magnon pairs, in the Ising-like chain antiferromagnet BaCo2V2O8. In large transverse fields, below the quantum critical point, we identify repulsively bound magnon states by comparing terahertz spectroscopy measurements to theoretical results for the Heisenberg-Ising chain antiferromagnet, a paradigmatic quantum many-body model2–5. Our experimental results show that these high-energy repulsively bound magnon states are well separated from continua, exhibit significant dynamical responses and, despite dissipation, are sufficiently long-lived to be identified. As the transport properties in spin chains can be altered by magnon bound states, we envision such states could serve as resources for magnonics based quantum information processing technologies6–8.