Strongly correlated systems far from equilibrium have recently generated considerable interest. This interest has mainly been spurred by experimental progress in preparing and characterizing such  systems out of equilibrum. The theoretical understanding on the other hand suffers from a lack of methods that can reliably treat strongly correlated systems in and out of equilibrium at an equal footing.Here, we present our results for the  thermal and non-thermal steady-state scaling functions and steady-state dynamics in a model of local quantum criticality. Our model, the pseudogap Kondo model, allows us to obtain full scaling functions in and out of equilibrium. We also study the concept of effective temperatures for correlations far from equilibrium near fully interacting as well as weak coupling fixed points. In the vicinity of each fixed point we establish the existence of an effective temperature –different at each fixed point–such that the equilibrium fluctuation-dissipation theorem is recovered. Most interestingly, steady-state scaling functions in terms of the effective temperatures coincide with the equilibrium scaling functions in terms of the equilibrium temperature. This result extends to higher correlation functions as will be explicitly demonstrated.

References:

- Non-linear quantum critical dynamics and fluctuation-dissipation ratios far from equilibrium

F. Zamani, P. Ribeiro, and S. Kirchner, J. Magn. Magn. Mat., 400, 7  (2016).

- Steady-State Dynamics and Effective Temperature for a Model of Quantum Criticality in an Open System

P. Ribeiro, F. Zamani, and S. Kirchner, Phys.~Rev.~Lett., 115,  220602 (2015).