Observation of 4- and 6-magnon bound-states in the spin-anisotropic frustrated antiferromagnet FeI${}_2$

Abstract

Spin-waves e.g. magnons are the conventional elementary excitations of ordered magnets. However, other possibilities exist. For instance, magnon bound-states can arise due to attractive magnon-magnon interactions and drastically impact the static and dynamic properties of materials. Here, we demonstrate a zoo of distinct multi-magnon quasiparticles in the frustrated spin-1 triangular antiferromagnet FeI${}_2$ using time-domain terahertz spectroscopy. The energy-magnetic field excitation spectrum contains signatures of one-, two-, four- and six-magnon bound-states, which we analyze using an exact diagonalization approach for a dilute gas of interacting magnons. The two-magnon single-ion bound states occur due to strong anisotropy and the preponderance of even higher order excitations arises from the tendency of the single-ion bound states to themselves form bound states due to their very flat dispersion. This menagerie of tunable interacting quasiparticles provides a unique platform in a condensed matter setting that is reminiscent of the few-body quantum phenomena central to cold-atom, nuclear, and particle physics experiments.

References in corpus (5)

• Hybridized quadrupolar excitations in the spin-anisotropic frustrated magnet FeI2
• Low Energy Electrodynamics of Novel Spin Excitations in the Quantum Spin Ice Yb${}_2$Ti${}_2$O${}_7$
• Dynamical signatures of quasiparticle interactions in quantum spin chains
• High order magnon bound states in the quasi-one-dimensional antiferromagnet $\alpha$-NaMnO${}_2$
• Magnetic-field-induced tunability of spin Hamiltonians: Resonances and Efimov states in Yb${}_2$Ti${}_2$O${}_7$

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• Refined Spin Wave Model and Multi-magnon Bound States in $L{i}_{2}Cu{O}_2$
• Quadrupole moments and their interactions in the triangular lattice antiferromagnet FeI${}_2$
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