Browsing by Author "Chung, C. H."

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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.
Strange superconductivity near an antiferromagnetic heavy-fermion quantum critical point
(2019-03-15)
Chang, Y. Y.
;
Hsu, F.
;
Kirchner, S.
;
Mou, C. Y.
;
Lee, T. K.
The heavy fermion systems CeMIn5 with M = Co, Rh, Ir, the "115" family, provide a prototypical example of strange superconductivity with unconventional d-wave pairing and strange metal normal state, emerged near an antiferromagnetic quantum critical point. The microscopic origin of strange superconductivity and its link to antiferromagnetic quantum criticality of the strange metal state are still long-standing open issues. We propose a microscopic mechanism for strange superconductors, based on the coexistence and competition between the Kondo correlation and the quasi-2d short-ranged antiferromagnetic resonating-valence-bond spin-liquid near the antiferromagnetic quantum critical point via a large-N Kondo-Heisenberg model and renormalization group analysis beyond the mean-field level. The interplay of these two effects provides a qualitative understanding on how superconductivity emerges from the strange metal state and the observed superconducting phase diagrams for CeMIn5.