The Effects of High Magnetic Fields on the Magnetic Excitations of Kondo Insulators

Spin-Excitons are sharp branches of dispersive triplet excitations found at excitation energies within the gap of paramagnetic Kondo Insulators. The spin-excitons are precursor excitations to an antiferromagnetic instability. In the presence of a weak magnetic field, the excitations are expected to split into three branches. Here we examine excitation energies and intensity of the spin-exciton branches as a function of the applied magnetic field. We find that the energy splittings of the dispersion relation are proportional to the applied field, and that the intensity of the lower branch diminishes rapidly with increasing fields.. For strongly-bound spin excitons, the lower branch softens with increasing field becoming a Goldstone mode of a field induced antiferromagnet phase. Furthermore, we find that for weakly-bound spin-excitons, the application of a sufficiently large applied field causes the intensity of the lowest energy branch to drop to zero resulting in a doublet of excitations.