The major effort in condensed matter physics is devoted to understanding and classifying the possible ground states and corresponding low-lying excitations that can emerge in interacting many-body systems. Physical properties of these states are usually described using linear-response theory, which assumes that the system is perturbed very weakly from its equilibrium state.
Recent remarkable advances in experimental techniques allow to probe and perturb conventional condensed matter systems on extremely short timescales and in an essentially non-linear regime. However, most conventional theoretical tools which successfully describe weak perturbations from equilibrium, break down in this context.
We are interested in developing theoretical understanding of the non-equilibrium/beyond-linear-response probes of solid state systems. In particular, we are looking for situations when non-equilibrium setups can provide new information that cannot be accessed using conventional probes.