Nonequilibrium finite-frequency noise of a resonance-level quantum dot close to a dissipative quantum phase transition: Functional Renormalization Group approaches

摘要

We calculate the finite-frequency current noise of a nonequilibriumresonance-level quantum dot close to a dissipative quantum phase transition ofthe Kosterlitz-Thouless (KT) type between a de-localized phase for weakdissipation and a localized phase for strong dissipation. The resonance-levelis coupled to two spinless fermionic baths with a finite bias voltage and anOhmic boson bath representing the dissipative environment. The system isequivalent to an effective anisotropic Kondo model out of equilibrium. Tocompute the finite-frequency noise, we combine two recently developedFunctional Renormalization Group (FRG) approaches in Refs.[17,22] and inRef.[23]. The nonequilibrium current noise at zero-temperature and finitefrequencies shows a singular dip in the de-localized phase for the magnitude offrequencies equal to the bias voltage; while the dip is smeared out as thesystem moves to the localized phase. The corresponding peak-to-dip crossover isfound in the AC conductance for the magnitude of frequencies equal to the biasvoltage. The relevance and applications of our results for the experiments andfor tunnelings between Fractional Quantum Hall Edge (FQHE) states and chiralLuttinger liquids are discussed.