Speck of chaos

It has been shown that a local perturbation applied to a single site of the one-dimensional XXZ model is enough to bring this interacting integrable spin-1/2 system to the chaotic regime. Here, we show that this is not unique to this model, but happens also to the Ising model in a transverse field and to the spin-1 Lai-Sutherland chain. The larger the system is, the smaller the amplitude of the local perturbation for the onset of chaos. We use these models to show the advantages of the correlation hole as a dynamical indicator of chaos that does not require unfolding the spectrum or separating it by symmetries. We compare it with an indicator of the eigenstate thermalization hypothesis, the Gaussian distribution of off-diagonal elements of local observables.