Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU
Dr Leonie Woodland, University of Oxford & ISIS Neutron and Muon Source, Rutherford Appleton Laboratory
Prof Amalia Coldea
Abstract
The excitations on an Ising chain are domain walls, which can form a variety of different bound states in the presence of additional interactions beyond the pure Ising limit. Here, we report inelastic neutron scattering measurements of the quasi-one-dimensional Ising-like ferromagnet CoNb2O6 to probe the evolution of the spectrum with field, which we understand in terms of these bound states.
In applied longitudinal field, the domain walls are confined into a Zeeman ladder, which we tune from weak confinement, where there are many closely spaced bound states, to strong confinement, where only two bound states remain, observing this crossover behaviour directly. We propose a model Hamiltonian that quantitatively reproduces all observed spectra in both high and low field applied along two orthogonal directions [1]. We also propose a new quantum mechanism of bound state formation between domain walls applicable for this Hamiltonian. The dispersions of the domain wall band can be tuned directly via an externally applied transverse magnetic field; we find that this tuning interplays with the inter-particle interactions to stabilize several bound states. These evolve in a non-trivial way as the applied magnetic field is varied, providing a natural explanation for the experimentally-observed field-dependence of the spectrum [2].
[1] L. Woodland, D. Macdougal, I. M. Cabrera, J. D. Thompson, D. Prabhakaran, R. I. Bewley, R. Coldea, Phys. Rev. B, 108 184416 (2023)
[2] L. Woodland, I. Lovas, M. Telling, D. Prabhakaran, L. Balents, R. Coldea, Phys. Rev. B, 108 184417 (2023)