Browsing by Author "Moca, C. P."

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Finite-frequency-dependent noise of a quantum dot in a magnetic field
(2014-04-29)
Moca, C. P.
;
Simon, P.
;
Chung, Chung-Hou
;
Zarand, G.
;
電子物理學系
We present a detailed study for the finite- frequency current noise of a Kondo quantum dot in the presence of a magnetic field by using a recently developed real- time functional renormalization group approach [C. P. Moca, P. Simon, C. H. Chung, and G. Zarand, Phys. Rev. B 83, 201303(R) (2011)]. The scaling equations are modified in an external magnetic field; the couplings and nonlocal current vertices become strongly anisotropic, and develop new singularities. Consequently, in addition to the natural emission threshold frequency, (sis) omega = | eV |, a corresponding singular behavior is found to emerge in the noise spectrum at frequencies (sis)omega approximate to | eV +/- B|. The predicted singularities are measurable with present- day experimental techniques.
Nonequilibrium frequency-dependent noise through a quantum dot: A real-time functional renormalization group approach
(2011-05-10)
Moca, C. P.
;
Simon, P.
;
Chung, C. H.
;
Zarand, G.
;
電子物理學系
We construct a real time current-conserving functional renormalization group (RG) scheme on the Keldysh contour to study frequency-dependent transport and noise through a quantum dot in the local moment regime. We find that the current vertex develops a nontrivial nonlocal structure in time that is governed by a new set of RG equations. Solving these RG equations, we compute the complete frequency and temperature dependence of the noise spectrum. For voltages that are large compared to the Kondo temperature (i.e., eV >> k(B)T(K)), two sharp antiresonances are found in the noise spectrum at frequencies h omega = +/- eV and, correspondingly, two Kondo-assisted peaks appear in the ac conductance through the dot.