Momentum-selective pair creation of spin excitations in dipolar bilayers

We study the temporal growth and spatial propagation of quantum correlations in a two-dimensional bilayer realising a spin-1/2 quantum XXZ model with couplings mediated by long-range and anisotropic dipolar interactions. Starting with an initial state consisting of spins with opposite magnetization in each of the layers, we predict the emergence of a momentum-dependent dynamic instability in the spin structure factor that results, at short times, in the creation of pairs of excitations at exponentially fast rates.