Non-equilibrium frequency-dependent noise through a quantum dot: A real time functional renormalization group approach

TL;DR

This paper develops a real-time functional renormalization group method on the Keldysh contour to analyze frequency-dependent noise and transport in a quantum dot, revealing non-trivial non-local current vertex structures and specific spectral features.

Contribution

It introduces a novel RG scheme that captures non-local temporal structures in quantum dot noise, providing detailed frequency and temperature dependence of the noise spectrum.

Findings

Sharp anti-resonances at frequencies ±eV in noise spectrum

Peaks in ac conductance at frequencies ±eV

RG equations reveal non-local current vertex structures

Abstract

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 non-trivial non-local structure in time, 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 large compared to the Kondo temperature, $eV \gg k_BT_K$, two sharp anti-resonances are found in the noise spectrum at frequencies $\hbar \omega = \pm e V$, and correspondingly, two peaks in the ac conductance through the dot.