Steady-state dynamics and effective temperatures of quantum criticality in an open system

TL;DR

This paper investigates the steady-state dynamics and effective temperatures in a quantum critical system modeled by the pseudogap Kondo model, revealing how effective temperatures restore fluctuation-dissipation relations and match equilibrium scaling functions.

Contribution

It demonstrates the existence of fixed-point-dependent effective temperatures that unify steady-state and equilibrium scaling behaviors in a quantum critical open system.

Findings

Effective temperatures exist near each fixed point.

Steady-state scaling functions match equilibrium ones when expressed with effective temperatures.

Non-linear charge transport can be described using the effective temperature.

Abstract

We study the thermal and non-thermal steady state scaling functions and the steady-state dynamics of a model of local quantum criticality. The model we consider, i.e. the pseudogap Kondo model, allows us to study the concept of effective temperatures 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 notably, steady-state scaling functions in terms of the effective temperatures coincide with the equilibrium scaling functions. This result extends to higher correlation functions as is explicitly demonstrated for the Kondo singlet strength. The non-linear charge transport is also studied and analyzed in terms of the effective temperature.