2025/10/23 by Satoshi Nishimoto, Nishimoto, Satoshi
Physics and Astronomy · #Physics of Superconductivity and Magnetism #Topological Materials and Phenomena #Cold Atom Physics and Bose-Einstein Condensates
paper · pdf · doi:10.48550/arxiv.2510.20633
We present a systematic study of multi-magnon bound states (MBSs) in the spin-\tfrac12 FM-AFM J1-J2 chain under magnetic fields using the density-matrix renormalization group method. As a quantitative measure of stability, we compute the magnon binding energy E\rm b(M,p) for bound clusters of size p over wide ranges of the frustration ratio J2/|J1| and the normalized magnetization M/M\rm s. Near saturation, we benchmark our data against the analytic two-magnon result and map out a clear hierarchy of p-magnon states, whose phase boundaries follow an empirical scaling J_2,\rm c(p;p + 1)/|J1| ≈ 0.34 p-2.3 for large p. We further quantify the relation between the most stable p and the zero-field pitch angle θ, verifying the conjectured inequality 1/p>θ/π>1/(p+1) up to p \lesssim 9. The binding energy shows pronounced suppression as J2/|J1| → 1/4+ and, for some frustration values, attains a maximum below full saturation, indicating that partial depolarization enhances bound-magnon mobility. Close to the FM instability, E\rm b(M\rm s,p) exhibits an empirical power-law vanishing consistent with a quantum-Lifshitz scenario. Our results provide a comprehensive, experimentally relevant map of MBS stability across field and frustration, offering concrete guidance for inelastic probes in quasi-one-dimensional magnets.