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The non-equilibrium quantum phase transitions are studied in two generic and relatively simple models: 1. a dissipative resonance-level quantum dot coupled to non-interacting Fermi liquid leads, and 2. a spinful quantum dot coupled to interacting one-dimensional electron leads. The first setup is mapped
onto an effective anisotropic Kondo model, leading to a quantum phase transition of the Kosterlitz-Thouless type between
the Kondo (conducting) and the local moment (insulating) phases.
The second setup exhibits either a conducting one-channel Kondo
(1CK) or an insulating two-channel Kondo (2CK) ground state,
as the Luttinger parameter K is decreased; the control parameter corresponds to the interaction strength in the 1d leads.
A quantum phase transition between 1CK and 2CK ground states is
reached when K=1/2. We apply a controlled frequency-dependent renormalization group approach to compute the non-equilibrium current in the presence of a finite bias voltage V
for both setups close to the phase transitions. For V → 0,
we find that the conductance in both cases has its well-known
equilibrium form, while it displays a distinct non-equilibrium
profile at finite voltage. To clarify the non-equilibrium quantum critical behaviors in these systems, we address the interplay
between non-equilibrium decoherence, Kondo entanglement and dissipation or Luttinger physics in these two systems.
References: 1. C-H Chung, K.V.P. Latha, K. Le Hur, M. Vojta, P. Woelfle, "Tunable Kondo-Luttinger system far from equilibrium", Phys. Rev. B 82, 115325 (2010), 2. Chung-Hou Chung, Karyn Le Hur, Matthias Vojta and Peter Woelfle, "Non-equilibrium transport at a dissipative quantum phase transition", Phys. Rev. Lett. 102, 216803 (2009). |
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