Abstract
Nonequilibrium properties of correlated quantum matter are being intensively investigated because of the rich interplay between external driving and the many-body correlations. Of particular interest is the nonequilibrium 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 nonequilibrium steady-state current in a critical system and experimental results to which the theory is compared. The system is a quantum dot coupled to resistive leads: a spinless resonant level interacting with an Ohmic dissipative environment. 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. As our system is fully accessible to both theory and experiment, it provides an ideal setting for addressing nonequilibrium phenomena in correlated quantum matter.Received 16 October 2020Revised 16 January 2021Accepted 21 January 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.013136Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCoulomb blockadeQuantum criticalityTransport phenomenaPhysical SystemsNanotubesQuantum dotsCondensed Matter, Materials & Applied PhysicsGeneral Physics
Highlights
Quantum phase transitions (QPTs)—abrupt changes of ground state due to quantum fluctuations—are of fundamental importance in a wide variety of many-body systems ranging from quantum materials to quantum magnets and nanostructures [1,2,3]
The system is a quantum dot coupled to resistive leads: a spinless resonant level interacting with an Ohmic dissipative environment
A two-channel Kondo-like quantum critical point (QCP) occurs when the level is on resonance and symmetrically coupled to the leads, conditions achieved by fine tuning using electrostatic gates
Summary
Quantum phase transitions (QPTs)—abrupt changes of ground state due to quantum fluctuations—are of fundamental importance in a wide variety of many-body systems ranging from quantum materials to quantum magnets and nanostructures [1,2,3]. These nanosystem QPTs provide insight into more complex quantum impurity QPTs, such as arise in strongly correlated materials [8,9,10,25] We present both an analytical calculation and a direct measurement of the steady-state current as a function of bias voltage (I-V curve) with system parameters tuned exactly to a QCP. Resonant peaks of perfect conductance in a LL have been extensively studied theoretically [36,37,38,39,40,41,42,43,44,45] This system has a similar two-channel Kondo-like QCP separating weaktunneling regimes dominated by one barrier, either source or drain [37,39,42]. Several Appendixes (Appendix A–G) present the details of our argument
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