Non-equilibrium quantum critical steady state: Transport through a dissipative resonant level

Non-equilibrium properties of correlated quantum matter are being intensively investigated because of the rich interplay between external driving and the many-body correlations [1]. Of particular interest is the non-equilibrium behavior near a quantum critical point (QCP), where the system is delicately balanced between different ground states. We present both an analytical calculation of the non-equilibrium steady-state current in a critical system and experimental results to which the theory is compared [2]. The system is a quantum dot coupled to resistive leads: a spinless resonant level interacting with an Ohmic dissipative environment [3]. A two-channel Kondo-like QCP occurs when the level is on resonance and symmetrically coupled to the leads, conditions achieved by fine tuning using electrostatic gates. We calculate and measure the nonlinear current as a function of bias (I-V curve) at the critical values of the gate voltages corresponding to the QCP. The quantitative agreement between the experimental data and the theory, with no fitting parameter, is excellent (Figure 1). As our system is fully accessible to both theory and experiment, it provides an ideal setting for addressing non-equilibrium phenomena in correlated quantum matter.

[1] 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).
[2] G. Zhang, C.-H. Chung*, C. T. Ke, C.-Y. Lin, H. Mebrahtu, A. I. Smirnov, G. Finkelstein*, H. U. Barangerar*, “Non-equilibrium quantum critical steady state: Transport through a dissipative resonant level”, Phys. Rev. Research 3, 013136 (2021).
[3] H. T. Mebrahtu, I. V. Borzenets, H. Zheng, Y. V. Bomze, A. I. Smirnov, S. Florens, H. U. Baranger, and G. Finkelstein, “Observation of Majorana quantum critical behavior in a resonant level coupled to a dissipative environment”, Nat. Phys. 9, 732 (2013).

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