Browsing by Author "Vojta, Matthias"

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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.
Quantum phase transitions in a resonant-level model with dissipation: Renormalization-group studies
(2007-12-01)
Chung, Chung-Hou
;
Glossop, Matthew T.
;
Fritz, Lars
;
Kircan, Marijana
;
Ingersent, Kevin
We study a spinless level that hybridizes with a fermionic band and is also coupled via its charge to a dissipative bosonic bath. We consider the general case of a power-law hybridization function Gamma(omega)proportional to vertical bar omega(r)vertical bar, with r >= 0, and a bosonic-bath spectral function B(omega)proportional to omega(s), with s >=-1. For r < 1 and max(0,2r-1)< s < 1, this Bose-Fermi quantum impurity model features a continuous zero-temperature transition between a delocalized phase, with tunneling between the impurity level and the band, and a localized phase, in which dissipation suppresses tunneling in the low-energy limit. The phase diagram and the critical behavior of the model are elucidated using perturbative and numerical renormalization-group techniques, between which there is excellent agreement in the appropriate regimes. For r=0, this model's critical properties coincide with those of the spin-boson and Ising Bose-Fermi Kondo models, as expected from bosonization.