Noninteger-spin magnonic excitations in untextured magnets
AbstractInteractions are responsible for intriguing physics, e.g., the emergence of exotic ground states and excitations, in a wide range of systems. Here, we theoretically demonstrate that dipole-dipole interactions lead to bosonic eigenexcitations with average spin ranging from zero to above ℏ in magnets with uniformly magnetized ground states. These exotic excitations can be interpreted as quantum coherent conglomerates of spin ℏ magnons, the eigenexcitations when the dipolar interactions are disregarded. We further find that the eigenmodes in an easy-axis antiferromagnet are spin-zero quasiparticles instead of the widely believed spin ±ℏ magnons. The latter reemerge when the symmetry is broken by a sufficiently large applied magnetic field. The average spin greater than ℏ is accompanied by vacuum fluctuations and may be considered to be a weak form of frustration.