In ordered quantum magnets where interactions between elementary excitations dominate over their kinetic energy, perturbative approaches often fail, making non-perturbative methods essential to capture spectral features such as bound states and the redistribution of weight within excitation continua. Although an increasing number of experiments report anomalous spin excitation continua in such systems, their microscopic interpretation remains an open challenge. Here, we investigate the spin dynamics of the triangular-lattice antiferromagnet in its 1/3-plateau phase using two complementary non-perturbative approaches: exact diagonalization in a truncated Hilbert space for a gas of elementary excitations (THED) and matrix product state (MPS) simulations. Alongside cross-validation between these methods, we benchmark our results against inelastic neutron scattering (INS) data. The THED analysis confirms the presence of two-magnon bound states and identifies the anomalous scattering continuum observed in both MPS and INS as a two-magnon resonance, arising from hybridization between the bound state and the two-magnon continuum. Furthermore, THED reveals bound states overlapping with the continuum, enriching the interpretation of continuum anomalies. More broadly, THED provides a robust framework for investigating anomalous spin excitation continua and bound-state effects in other materials with gapped spectra. Its combination of accuracy and computational efficiency makes it a powerful tool for extracting reliable microscopic models in semiclassical regimes.

Electron charging plays a key role in physicochemical processes, whose intrinsic stabilization in single molecules is desirable for tailoring molecular functionality and developing molecular devices, but remains elusive on surfaces. Here, we show that molecular charge states can be self-stabilized via intramolecular distortion in single bis(phthalocyaninato)terbium(III) (TbPc2) double-decker molecules, which were grown on the Pb(111) substrate. Using scanning tunneling microscopy and spectroscopy, we identify fractions of TbPc2 molecules that reduce to 2-fold symmetry, exhibiting energy-split molecular orbitals and two types of different spin states. Our first-principles calculations unveil that the symmetry reduction is induced by charging-triggered Jahn-Teller distortions, which lift the degenerate orbitals into two 2-fold symmetric orbitals. Single or double occupancy of the lower-energy orbital results in different molecular spin states. Such intramolecular distortion traps the excess electrons stably without explicit involvement of the substrate, in contrast to previously observed molecular charge states. These charged single molecules can be manipulated with the tip individually. This study offers a new avenue for tailoring the charge and spin states of molecules.

YbFeO3 is exceptional among the rare-earth orthoferrites for having the lowest spin-reorientation transition (SRT) temperature, T-SRT similar or equal to 8K, which makes it particularly appealing to examine the interplay between noncollinear magnetism of the Fe sublattice and quasi-one-dimensional XXZ effective S = 1/2 chains of Yb3+ moments. Our paper focuses on the magnetic dynamics of YbFeO3 using inelastic neutron scattering (INS), at temperatures below and above the SRT, under an applied hydrostatic pressure of 2 GPa, and in magnetic fields up to 4 T. The low-energy zero-field excitation spectrum at ambient pressure and temperatures below the SRT is dominated by a gapped magnon mode of the Yb subsystem at 0.84 meV with a dispersion only in the [00L] direction. Above T-SRT, a continuum appears on top of the magnon mode because of temperature population of the magnon band, and the gap decreases to around 0.4 meV. The INS spectra in the magnetic field, both above and below T-SRT, are characterized by two well-separated gapped modes. The SRT is clearly visible at low fields B < 1 T, but it gradually disappears at higher magnetic fields. The hydrostatic pressure of p = 2GPa effectively reduces the transition width, Delta T-SRT, and keeps the SRT at higher fields up to B similar or equal to 3 T. We discuss the effect of the applied pressure in the frame of the modified mean-field theory and show that in the vicinity of the T-SRT the pressure tunes the fourth-order anisotropy constant that effectively reduces the Delta T-SRT.

CsYbSe2 Tao Xie, ∗ Jie Xing, ∗ S. E. Nikitin, S. Nishimoto, 5 M. Brando, P. Khanenko, J. Sichelschmidt, L. D. Sanjeewa, Athena S. Sefat, and A. Podlesnyak Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Paul Scherrer Institut, CH-5232 Villigen, Switzerland Department of Physics, Technical University Dresden, 01069 Dresden, Germany Institute for Theoretical Solid State Physics, IFW Dresden, 01069 Dresden, Germany Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany