Confinement of fractional excitations in a triangular lattice antiferromagnet

Abstract

High-resolution neutron and THz spectroscopies are used to study the magnetic excitation spectrum of Cs${}_2$CoBr${}_4$, a distorted-triangular-lattice antiferromagnet with nearly XY-type anisotropy. What was previously thought of as a broad excitation continuum [Phys. Rev. Lett. 129, 087201 (2022)] is shown to be a series of dispersive bound states reminiscent of "Zeeman ladders" in quasi-one-dimensional Ising systems. At wave vectors where inter-chain interactions cancel at the Mean Field level, they can indeed be interpreted as bound finite-width kinks in individual chains. Elsewhere in the Brillouin zone their true two-dimensional structure and propagation are revealed.

arXiv comment11 pages, 8 figures

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• Spin-flop-like transition as quantum critical point in Cs${}_2$RuO${}_4$
• Magnetic phase diagram and spin Hamiltonian of antiferromagnet Cs${}_2$CoI${}_4$
• Competing states in the $S=1/2$ triangular-lattice $J_1$-$J_2$ Heisenberg model: a dynamical density-matrix renormalization group study