Amplitude mode in two-dimensional coherent spectroscopy of weak-coupling antiferromagnets

Abstract

Two-dimensional coherent spectroscopy (2DCS) provides insights into the nonlinear response of correlated lattice systems. We simulate multipulse excitations in the Hubbard model using nonequilibrium dynamical mean-field theory to extract the 2DCS signal of weak-coupling antiferromagnets with and without local potential disorder. By comparing calculations with static and dynamic Hartree terms, and analyzing the waiting-time dependence of the signal, we identify the contribution of the collective amplitude mode to the spectroscopic features and the relevant underlying processes. With broadband pulses, the rephasing and nonrephasing peaks at the gap energy are found to be of predominant amplitude mode character. Using narrow-band pulses, we also demonstrate a strong enhancement of these amplitude mode-related signals at a pulse frequency of half the gap size.