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

TL;DR

This paper investigates the finite-frequency current noise in a dissipative quantum dot near a Kosterlitz-Thouless transition, revealing a dip at bias voltage frequency that varies with dissipation strength, using advanced FRG methods.

Contribution

It introduces a combined FRG approach to analyze nonequilibrium noise in a quantum dot near a KT transition, linking dissipative effects to observable noise features.

Findings

Singular dip in noise at bias voltage in the delocalized phase

Dip smears out as system approaches localized phase

Peak-to-dip crossover observed in AC conductance

Abstract

We calculate the finite-frequency current noise of a nonequilibrium resonance-level quantum dot close to a dissipative quantum phase transition of the Kosterlitz-Thouless (KT) type between a de-localized phase for weak dissipation and a localized phase for strong dissipation. The resonance-level is coupled to two spinless fermionic baths with a finite bias voltage and an Ohmic boson bath representing the dissipative environment. The system is equivalent to an effective anisotropic Kondo model out of equilibrium. To compute the finite-frequency noise, we combine two recently developed Functional Renormalization Group (FRG) approaches in Refs.[17,22] and in Ref.[23]. The nonequilibrium current noise at zero-temperature and finite frequencies shows a singular dip in the de-localized phase for the magnitude of frequencies equal to the bias voltage; while the dip is smeared out as the system moves to the localized phase. The corresponding peak-to-dip crossover is found in the AC conductance for the magnitude of frequencies equal to the bias voltage. The relevance and applications of our results for the experiments and for tunnelings between Fractional Quantum Hall Edge (FQHE) states and chiral Luttinger liquids are discussed.