Spectral Signatures of Quasiparticle Interactions in Antiferromagnets

Elementary excitations in quantum magnets can be typically described in terms of long-lived quasiparticles, either simple magnons (spin waves), or more exotic fractionalized excitations such as spinons. In general, when multiple quasiparticles are present, they interact, and in a strongly correlated system, they interact strongly.
In this talk I will discuss signatures of interactions between quasiparticles that show up in the dynamical spin correlations of antiferromagnets in presence of a magnetic field. I will first focus on our study of the antiferromagnetic spin-1/2 chain, a paradigmatic model of strongly correlated systems which is known to host fractionalized spinon excitations. I will address both the low and high magnetization regimes. In the low magnetization regime, in the gapless phase, we find that the marginally irrelevant backscattering interaction between the spinons leaves a distinct signature in the transverse dynamical susceptibility creating a non-zero gap between two branches of excitations at small momentum. In the high magnetization regime, close to the saturation field, we show that interactions between magnons lead to a formation of two-magnon bound states which leave a sharp feature in the transverse correlations. I will then address higher-dimensional systems and argue that these observations are not unique to 1D.

Link to zoom