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

Area of Science:

• Condensed Matter Physics
• Quantum Criticality
• Statistical Mechanics

Background:

• Understanding steady-state properties of quantum systems far from equilibrium is a significant challenge.
• Local quantum criticality provides a framework to study non-equilibrium phenomena.
• The pseudogap Kondo model offers a tractable system for investigating these complex behaviors.

Purpose of the Study:

• To investigate thermal and nonthermal steady-state scaling functions in a model of local quantum criticality.
• To explore the concept and application of effective temperatures in non-equilibrium systems.
• To determine if equilibrium properties can be recovered in the steady state using effective temperatures.

Main Methods:

• Utilized the pseudogap Kondo model to analyze steady-state dynamics.
• Established the existence of effective temperatures near interacting and weak-coupling fixed points.
• Calculated and compared steady-state scaling functions with equilibrium counterparts.

Main Results:

• An effective temperature was identified for each fixed point, recovering the equilibrium fluctuation-dissipation theorem.
• Steady-state scaling functions, expressed in terms of effective temperatures, were found to coincide with equilibrium scaling functions.
• This universality was confirmed for higher correlation functions, including Kondo singlet strength, and nonlinear charge transport.

Conclusions:

• Effective temperatures provide a powerful tool for characterizing non-equilibrium steady states in quantum critical systems.
• The study demonstrates a remarkable convergence of steady-state and equilibrium scaling behaviors under the effective temperature framework.
• These findings offer new insights into universal properties of quantum matter in and out of equilibrium.