Browsing by Author "Woelfle, Peter"

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Nonequilibrium quantum transport through a dissipative resonant level
(2013-06-21)
Chung, Chung-Hou
;
Le Hur, Karyn
;
Finkelstein, Gleb
;
Vojta, Matthias
;
Woelfle, Peter
The resonant-level model represents a paradigmatic quantum system which serves as a basis for many other quantum impurity models. We provide a comprehensive analysis of the nonequilibrium transport near a quantum phase transition in a spinless dissipative resonant-level model, extending earlier work [Phys. Rev. Lett 102, 216803 (2009)]. A detailed derivation of a rigorous mapping of our system onto an effective Kondo model is presented. A controlled energy-dependent renormalization-group approach is applied to compute the nonequilibrium current in the presence of a finite bias voltage V. In the linear-response regime V -> 0, the system exhibits as a function of the dissipative strength a localized-delocalized quantum transition of the Kosterlitz-Thouless (KT) type. We address fundamental issues of the nonequilibrium transport near the quantum phase transition: Does the bias voltage play the same role as temperature to smear out the transition? What is the scaling of the nonequilibrium conductance near the transition? At finite temperatures, we show that the conductance follows the equilibrium scaling for V < T, while it obeys a distinct nonequilibrium profile for V > T. We furthermore provide different signatures of the transition in the finite-frequency current noise and ac conductance via a recently developed functional renormalization group (FRG) approach. The generalization of our analysis to nonequilibrium transport through a resonant level coupled to two chiral Luttinger liquid leads, generated by fractional quantum Hall edge states, is discussed. Our work on the dissipative resonant level has direct relevance to experiments on a quantum dot coupled to a resistive environment, such as H. Mebrahtu et al., [Nature (London) 488, 61 (2012)].
Nonequilibrium Transport at a Dissipative Quantum Phase Transition
(2009-05-29)
Chung, Chung-Hou
;
Le Hur, Karyn
;
Vojta, Matthias
;
Woelfle, Peter
;
電子物理學系
We investigate the nonequilibrium transport near a quantum phase transition in a generic and relatively simple model, the dissipative resonant level model, that has many applications for nanosystems. We formulate a rigorous mapping and apply a controlled frequency-dependent renormalization group approach to compute the nonequilibrium current in the presence of a finite bias voltage V and a finite temperature T. For V -> 0, we find that the conductance has its well-known equilibrium form, while it displays a distinct nonequilibrium profile at finite voltage.
Two-stage Kondo effect in side-coupled quantum dots: Renormalized perturbative scaling theory and numerical renormalization group analysis
(2008-01-01)
Chung, Chung-Hou
;
Zarand, Gergely
;
Woelfle, Peter
;
電子物理學系
;
Department of Electrophysics
We study numerically and analytically the dynamical (ac) conductance through a two-dot system, where only one of the dots is coupled to the leads but it is also side coupled to the other dot through an antiferromagnetic exchange Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. In this case, the RKKY interaction gives rise to a "two-stage Kondo effect" where the two spins are screened by two consecutive Kondo effects. We formulate a renormalized scaling theory that captures remarkably well the crossover from the strongly conductive correlated regime to the low temperature, low conductance state. Our analytical formulas agree well with our numerical renormalization group results. The frequency-dependent current noise spectrum is also discussed.